Between 1616 and 1618, a very curious motif combining a Medusa head with Jupiter’s thunderbolt appears on shields depicted by Rubens in numerous paintings, such as The Obsequies of Decius Mus from the Liechtenstein Collection,1Decius Mus Addressing the Legions in the National Gallery, Washington D.C.,2 and the approximately contemporaneous Achilles Discovered by Ulysses and Diomedes in the Museo Nacional del Prado.3

The study of the artist’s method of juxtaposing selected texts and images in his works has consistently revealed Rubens’s impressive knowledge of the ancient world, his erudition, and his mastery of the classical literary tradition. In recent decades Rubens’s fame as pictor doctus has become a commonplace in scholarship on the artist. Several art historians have demonstrated that his intellectual and self-conscious agency influenced his inventiveness and artistic creativity,4 his choices as an art and book collector,5 and the entire decorative program of his magnificent house in Antwerp.6 Rubens’s large house with its rich ornamentation inspired by Antiquity, the art collection, and the library seem an attempt to embody the entire encyclopedia of human knowledge, offering insight into Rubens as an artist with humanist leanings who also cherished living classical heritage. His surviving sketchbooks, where he kept his drawings and his notes, as well as his vast – but only partially preserved – correspondence further attest to his constant rethinking of iconographical themes on the basis of his exceptional training in texts. This large body of evidence shows that Rubens imbued his art with theory, and that he deployed the encyclopedic knowledge of his age to generate artistic invention.7 Rubens embodied the Renaissance idea of the learned painter, a highly theoretical man who possessed knowledge in a wide range of fields, such as optics, proportions, anatomy, architecture, natural philosophy, and theology. His extensive and erudite use of classical heritage and its subsequent reworking, in addition to demonstrating his ingenium,8 resulted from the importance he placed on the Renaissance theory of artistic imitation and the role this had in his discovery of the rules for the imitation of nature.9

Moreover, the principle of imitating nature is a manifestation of a philosophical attitude rooted in Neostoicism. According to Justus Lipsius, the Flemish scholar responsible for the Stoic revival at the end of the sixteenth century, wisdom was acquired by studying the hidden structure of nature. For the Stoic philosopher ‘living according to nature’ led men to the achievement of virtue and reason. Relying on the teachings of Seneca, ‘Lipsius was perhaps the first modern European to recognize clearly […] that the heart of Stoicism is not its ethics but its philosophy of nature’.10 Lipsius developed this theme most fully in his Physiologia Stoicorum (Antwerp, 1604), a work Rubens was surely familiar with.11 The artist would have known about these moral precepts and philosophical rules through the cultivation of his friendship with Lipsius as well as from his older brother Philip, as attested to in his two self-portraits showing the men together: the Mantuan Friendship Portrait and the Four Philosophers.12 These pictures proclaim Rubens’s knowledge of and adherence to Neostoic principles. Rubens’s philosophical ambitions were acknowledged by his close friend and correspondent Johann Faber; in his treatise on Mexican animals published in 1628 the German physician refers to the brothers Rubens, calling them both disciples of Lipsius, and worthy successors of his chair.13

Rubens’s friendship with Faber evidences the artist’s engagement with the Lincean Academy in Rome, of whom Faber was a member, and which was one of the earliest scientific societies for the transmission of secret knowledge,14 principally focused on natural philosophy, Platonic philosophy, Hermeticism, and Paracelsianism. As Frances Huemer has outlined, the Lincean Academy took a Neostoic position during its early years, and its members were in several ways influenced by Lipsius’s philosophy.15 The relationships and cultural exchanges between intellectuals in Rome and north of the Alps should not come as a surprise, since both the Lincean society and Lipsius’s Neostoic circle shared a common interest in the acquisition of knowledge through the study of nature.16 Recent research has also shed light on the particular interest in and circulation of Platonic, Neopythagorean, and Hermetic themes, as well as Aristotelian, Neostoic, and Paracelsian ideas in the first years of activity of the Lincean Academy (1603–1616).17

The well-developed system of connections between intellectuals throughout Europe contributed to the birth of a universal philosophy of nature in which various occult traditions are visible. Hermetic and Neoplatonic influences are present in Lipsius’s works18 and in Rubens’s so-called Theoretical notebook or Pocket Book,19 attesting to the authors’ fruitful contacts with the Lincean circle of humanists. This Theoretical notebook, composed by Rubens during the course of his life, also gives clear evidence of his intellectual interests in natural philosophy, Christian Cabala, and ideas drawn from Paracelsian alchemy and Pythagorean number mysticism.20 Rubens’s notes, in which he draws analogies and correspondences between geometric figures and body parts, are rooted in the intellectual environment of the end of the sixteenth century in which Neoplatonism and a focus on the observation of nature were combined. In particular, the belief in a cyclic connection between all beings, animated and not, was established in the natural magic practiced by the Italian philosophers Giovan Battista Della Porta, Giordano Bruno, Niccolò Antonio Stigliola, and Tommaso Campanella, and by Rubens’s German friend Johann Faber in Rome.21 These intellectuals were members of the Lincean Academy or were directly connected with the institution. Moreover, they all maintained contacts with European scholars and artists directly or through the numerous German and Dutch Lincei as intermediaries.22

As a member of the European network of erudite connoisseurs that had come into being during the second half of the sixteenth century, Rubens contributed to the circulation of knowledge through his artworks, letters, and notebooks. When dealing with his works we should bear in mind, rather than Horace’s famous ut pictura poesis which emphasizes the analogy between painting and poetry,23 a broader, more inclusive concept outlined by Giordano Bruno at the end of the sixteenth century, according to which ‘philosophers are in some ways painters and poets; poets are painters and philosophers; painters are philosophers and poets. Whence true poets, true painters, and true philosophers choose one another out and admire one another.’24 This almost ubiquitous association between philosophers, poets, and painters by critics and intellectuals of the sixteenth century was anchored in the shared vividness of their imagery, the thought processes through which they worked, and their commitment to the study and imitation of nature.25 During the Renaissance both texts and images were infused with philosophical and moral convictions; every learned man pursued the quest for universal truth and moral regeneration. As befitted a pictor doctus living in the early seventeenth century, Rubens imbued his art with the poetic spirit and the philosophical ideas characteristic of his time.

This article provides a detailed analysis of a motif depicted by Rubens on ancient shields between 1616 and 1618. The first section examines the ancient origin of the motif and the variations the artist subsequently devised for his paintings; the second deals in particular with the Homeric description of shields, which were understood as allegories of the cosmos. The article also considers the specific significance of this motif in the context of the stories of Decius Mus and Achilles. Finally, the third section examines how Rubens’s knowledge of Lipsius’s natural philosophy and cosmology on Neoplatonic, Hermetic, and cabalistic grounds influenced his process of artistic invention.

Rubens’s Reception of an Antique Motif on Shields

The first time the motif of a Medusa head with Jupiter’s thunderbolt appears on ancient shields in Rubens’s oeuvre is on a drawing now conserved in the Louvre, which is a fragment cut from an unidentified battle scene (fig. 1).26 This drawing, known in the Louvre catalogues as Battle between infantry and horsemen or A Battle between Romans and Barbarians, came from the collection of Everhard Jabach (1618–1695).27 In 1949 the collector and connoisseur Frits Lugt noted details in the pen- and brushstrokes that betrayed the hand of Rubens, and he classified the picture as ‘retouched by Rubens’.28 In the 1978 catalogue of drawings by Polidoro da Caravaggio, however, this battle piece was identified by Lanfranco Ravelli as a copy by Rubens after a lost composition by Polidoro.29 Some years earlier, Michael Jaffé proposed it to be in fact a Rubens autograph, representing ‘a brilliant exercise by Rubens in his Polidoresque vein’.30 More recently, Lugt’s original assertion that the Battle between Infantry and Horsemen was only retouched by our artist was reconfirmed by Jeremy Wood, who also published another copy of the same composition that he attributes simply to an anonymous Italian sixteenth-century artist.31

Fig. 1 

Anonymous Italian artist (retouched by Rubens), Battle between infantry and horsemen, late 16TH century, drawing in pen and brown and black ink, 22,5 x 38,0 cm, Paris © RMN-Grand Palais (Musée du Louvre)/Michèle Bellot.

This leads us to conclude that Rubens took the motif from the late sixteenth-century drawing that he retouched, and that the author of that drawing must have taken it from some ancient source. This fragment of a larger sheet, once owned and retouched by Rubens, was produced within the circle of Polidoro da Caravaggio, a pupil of Raphael. That being the case, it is perhaps in Raphael’s school that the motif of Medusa over the thunderbolt was first copied from an ancient precedent. Giulio Romano included the thunderbolt and Medusa’s head on shields both in his frieze of a Roman army on the march in the Camera degli Stucchi of the Palazzo Té as well as in his tapestry cycle of the Life of Scipio in Mantua; these symbols are, however, never joined together.32 No other sixteenth or seventeenth-century drawing or print in which this motif recurs is known to me, apart from the drawing retouched by Rubens. It is therefore most likely that Rubens took the motif from that drawing and that its producer borrowed it from an ancient source, since there is ancient precedent.

In fact, the combination of the Medusa head with Jupiter’s thunderbolt appears during the Hellenistic period. It occurs, for instance, on early third-century terracotta miniature shields from the Tomb of the Erotes at Eretria, in Greece (fig. 2). Discovered by the end of the nineteenth century, the tomb group includes terracotta figurines, gold diadems, earrings, rings, and bracelets, as well as twenty-eight miniature round and oval terracotta shields, decorated in relief with thunderbolts, stars, rays and six variations on the heads of Alexander the Great, Helios, the Dioskouroi, and Medusa.33 These small reliefs (9–10 cm) are stylistically dated to the early Hellenistic period, ca. 375–325 BC. The 1980–1982 exhibition The Search for Alexander included examples of the terracotta figurines and the shield reliefs, and displayed them with the jewelry from the tomb.34 Examples of these various objects from the Tomb of the Erotes in the collection of the Museum of Fine Arts in Boston have appeared in various publications, although the tomb and its contents were not fully published until 2008.35 The sixteenth-century Italian author of the Louvre drawing probably saw an original Hellenistic prototype that Rubens eventually first retouched and then used with some variations as a motif in his painting compositions. During Rubens’s lifetime only a few Classical or Hellenistic Greek antiquities were known; most of them survived only in copies of the Roman period.36 It is possible that the anonymous artist of the battle scene took his inspiration from sixteenth and seventeenth-century collections of antiquities in which Hellenistic prototypes (coins, sculptures, mosaics, and paintings) were conserved.

Fig. 2 

Miniature-shields showing Medusa with thunderbolt, Greek Hellenistic Period (310–240 BC), terracotta, 9–10 cm, Boston, MFA © Catharine Page Perkins Fund.

In any case this motif, copied by Rubens from an Italian artist, is certainly based on terracotta votive shields, and in particular on the small almond-shaped shields of the so-called Gallic or Galatian type, with a snaky-locked Gorgon set against a full thunderbolt, with its flashes of lightning.37 This type of shield appears in Greece in the third century, and was probably brought into the Greek repertory by the Gauls.38 The thunderbolt or the ‘the winged shaft of Zeus’ is an apt ornament for the shield.39 The winged head of the Gorgon, with snakes instead of hair, is frequently depicted from the fourth century BC onwards, and is typical of the Hellenistic period. The juxtaposition of Medusa on thunderbolt refers to two different symbols of Zeus’s power, the severed head of the Gorgon having been originally fixed on Athena’s aegis-mantle (a goatskin, in this case transformed into a shield), which the goddess had inherited from Zeus. The Gorgon on a thunderbolt can therefore be considered as a terrific apotropaion, doubly blinding and petrifying.

Rubens must have accorded both symbols a specific significance, since several years after his retouching of the anonymous battle scene he recuperated the motif from the drawing and depicted it on shields in the paintings of the Decius Mus series and in the Achilles painting. These shields were no longer of the Gallic type, but rather round and convex, the so-called Argive type. They also displayed the combination of the Gorgon’s head with the thunderbolt, but in contrast to the classical prototypes Rubens arranged the flashes of lightning in the form of the sun or a star. Moreover, in Decius Mus Addressing the Legions and in the Achilles painting, Rubens added a mature beard with moustache to the female head of the Gorgon, which in these cases is also accompanied by the thunderbolt and the flashes of lightning (figs. 3 and 4). Representations of masculine Gorgons were not common in Antiquity; only a few male gorgoneia are known and they were the result of contaminations from other divinities in the classical pantheon.40 It is not known if Rubens was aware of these variations on the standard depiction of Medusa, but this was not the first time that the artist had realized a sex change in his artistic production. In several drawings after Italian masters in particular, Rubens transformed or changed the sex of the figures while retouching.41 This can be understood as a sign of Rubens’s self-conscious inventio, but also as a way of expressing a specific message. If the latter is the case, Rubens perhaps took his inspiration for this ‘contaminated Medusa’ from the literary tradition. It is indeed well-known that the artist juxtaposed selected texts and images in his works and that his engagement with ancient authors shaped his visual language.42 The following section will therefore analyze several classical texts describing decorated shields in military contexts.

Fig. 3 

Peter Paul Rubens and workshop (Anthony Van Dyck?), Achilles Discovered by Ulysses and Diomedes, ca. 1617–1618, oil on canvas, 248,5 x 269,5 cm, Madrid © Museo Nacional del Prado.

Fig. 4 

Peter Paul Rubens, Decius Mus Addressing the Legions, ca. 1616, oil on hardboard, 80,7 x 84,7 cm, Washington D.C., National Gallery of Art © Samuel H. Kress Collection.

The Poetics of Homer’s Description and the Case of Rubens’s Shield

The classical motif of the disembodied, frontal head occurs on coinage as well as in military contexts. First introduced into Greek art as early as the eighth century BC, this motif had a particularly religious significance. The most common use of the type was that of the gorgoneion, or head of Medusa severed by the hero Perseus, which was adopted by the goddess Athena as the central device of her shield or aegis.43 Depicted with a hideous visage, which included wide eyes, protruding tongue, and snaky hair, the gorgoneion had the ability to ward off the evil eye. It was therefore also placed on doors, tombstones, and military equipment, locations where such protection was particularly necessary. For their apotropaic character gorgoneia also decorated military shields. Epic poems from ancient literature vividly describe the decoration of kings’ or heroes’ shields: a gorgoneion decorated Agamemnon’s shield in the Iliad and Athena’s aegis to terrify her enemies.44 In Homer’s account of Agamemnon’s preparation for battle, the great poet describes the terrifying look of the Gorgon on the Greek hero’s shield, adding that Medusa was flanked by Horror and Fear (Deinós and Phobos).45 In the form of a lion’s head, Fear also adorns a shield of Agamemnon on the chest of Cypselus in Pausanias’s description.46

Fear is thus one of the personifications found on great warriors’ shields in Greek narratives, and it clearly occupies the center of the shield in Rubens’s The Obsequies of Decius Mus (fig. 5). The intimidating and fearsome gaze of the Gorgon on Decius Mus’s shield recalls Homer’s ekphrastic description of Agamemnon’s shield. The themes of fear and strife fit in well with Stoic discourse, in which these passions are responsible for the annihilation of man’s wisdom. Stoicism required men to overcome fear to succeed in battle. In The Obsequies of Decius Mus, the Gorgon’s terrifying gaze is paralyzing, disabling men from acting or speaking, and clearly serves an important function in the context of the heroic death of the Roman consul.47 The presence of the thunderbolt and the flashes of lightning, together with the facing head, seems to reflect Rubens’s reliance on Homer’s ekphrastic descriptions, in which gods and kings were described as being surrounded by a cloud of fiery power, a symbol of their glory and a source of terror that overthrows the enemy. Majestic glory evokes both wonder and fear. The Greek epics associate divine radiance, and the ability to instill terror, with the armor and weapons of those who bear such luminous appearance.48 Homer narrates that Achilles’s armor, forged by Hephaestus, ‘flashes like the sun, moon, or fire’.49 This Homeric motif is repeated by Virgil in the description of Aeneas’s flashing armor, ‘shooting quivering thunderbolts from his shield’.50 The light that shoots from the shield of Achilles and the flames that pour from Aeneas’s shield suggest an identification with Zeus, the wielder of the thunderbolt. This imagery also suggests divine epiphany, the miraculous and terrifying appearance of the gods announced by thunder, lightning, and thick clouds.51 Homer uses the word enargeia, derived from argos meaning ‘radiant’, to describe the shining appearance of the gods.52

Fig. 5 

Peter Paul Rubens, The Obsequies of Decius Mus, ca. 1616–1617, oil on canvas, 289 x 515 cm © Liechtenstein, The Princely Collections, Vaduz-Vienna/SCALA, Firenze.

After all, Lipsius required Rubens and his other students to read the classical poems of Homer, Virgil, and others ‘as a way of showing that the myths pertaining to the gods were not literally true, but bespoke a more rational view of the cosmos in which the gods and myths allegorized natural forces or physical moral truths’.53 There was a long Stoic tradition of analyzing the allegorical meanings of myths, in which the gods became symbols for cosmic powers and each tale concealed a truth about a natural phenomenon.54 As a professed Lipsian Stoic, Rubens introduced the thunderbolt on the shield to allude to the presence of the divinity, which guarantees protection and support to the gods’ chosen ones but also spreads fear and terror, resulting in the defeat of the enemy in battle. Both Achilles and Decius Mus are heroes protected by the gods; they can count on divine benevolence because of their own wisdom and courage. The presence of the gods inspires both fear and admiration; it is marvelous and awful at the same time; it can both save and destroy.

The Homeric heroes claim their direct descent from Zeus, the king of the gods, and thus bear the fiery name Aithon.55 This term denotes a ruler and intimates the protection Zeus gives to his people. The name Aithon, employed by Ulysses and other Homeric characters, also refers to Zeus’s thunderbolt, the weapon he uses to punish offenders. The word itself is associated with fire and lightning and derives from the Greek root αἴθω which means ‘to burn’, but as convincingly argued by Olga Levaniouk, the word covers a wider range of meanings, referring to the ‘fiery, burning’ temperament of the Homeric heroes, and is also used to describe the flickering, blazing light reflected from burnished metals.56

From the same root also originates the word aether (αἰθήρ), which denotes the bright realm of the sky and Zeus’s kingdom.57 In Homer, the shining and flashing light of the heroes’ weapons clearly indicates the ‘divine origin’ of these artefacts and their bearers. The combination of mythological and cosmological aspects becomes even clearer in Homer’s description of Achilles’s famous shield, which the poet compares with the heavenly bodies: ‘a star, or the sun, or the moon. It seems therefore plausible that the astronomical character of the Homeric shield inspired the star-shaped symbol adorning Rubens’ shields. Achilles’s shield is an image of the order of the universe, and its symbolism turns out to be intimately connected to its cosmological significance.58 After all, Homer applied his celestial imagery to objects having divine significance. The astronomical imagery of the shield also appears in Virgil, who describes Aeneas’s star-shield or patrium sidus. Virgil’s use of the word sidereo in describing Aeneas’s shield has been interpreted by some scholars as an indication of the divine nature of the hero’s armor.59 Likewise, Rubens’s starry shield should be seen as a symbol of divine power, coming down from heaven. At the same time, the shield is an allegory of the whole universe, the cosmos, as the presence of the ouroboros surrounding the human head in the Madrid Achilles painting seems to suggest.60 Again Rubens creates his images by taking inspiration from ekphrastic poetry: following the dictum ut pictura poesis the artist translates mute poetry into a speaking masterpiece by his brush. The poetic description of the Homeric shield was interpreted by ancient and modern critics as a literary microcosm (clipeus vasti caelatus imagine mundi).61

Inspired by Homer’s literary passage, Ovid reworks the shield as iconic artefact with prophetic qualities. In book 13 of the Metamorphoses, the Roman poet alludes to the shield as a paradigm of creation, emphasizing the relationship and mutual correspondence between the artistry of the creator and the creativity of the artist, a theme that was very dear to Rubens.62 Ovid presents the shield as a powerful predictive object; it reflects the future of the heroes and their descendants. In direct line with Ovid’s interpretation of the Homeric passages, Rubens introduces the subject of destiny into his work. In his Achilles painting the Flemish master chooses to depict the episode in which the Greek hero, disguised as a maiden, was hidden at the court of King Lycomedes, in order to avoid his fate and die at Troy.63 Ovid narrates that Ulysses and Diomedes were cognizant of this plot and wanted Achilles to help them fight the war. Disguised as merchants, they offered certain gifts to Lycomedes’s daughters as a way of disclosing the truth. As they had hoped, the hero revealed his true sex by showing interest in the weapons they had included, rather than the jewels and other female adornments. Rubens depicted the exact moment that Ulysses denounces Achilles as he unsheathes a sword and calls him to fight against the Trojans.64 The weapons and the shield in Rubens’s painting illuminate the destiny of Achilles, guiding him towards his path: brief and noble glory in war instead of a peaceful old age at home.65 Achilles’s armor embodies the prophesied fate of the hero, which will lead him to the victory. The story of the Roman consul Decius Mus is similarly dominated by prophecies. According to Livy’s narration, the victory of the Romans in war against the Latins (340 BC) was only guaranteed through the self-sacrifice of the consul Decius Mus, as had been foretold by the combination of a prophetic dream and a haruspical response.66 From the interpretation of auguries Decius understood that he had to perform the process of vowing himself to death (devotio) and lose his life to ensure his army’s victory.67 He performed his act of piety during the battle, by riding headlong into the enemy ranks, and the Romans won.

Rubens was the first artist to translate into painting Livy’s account of the war between the Romans and the Latins. In several episodes of the story, he introduces the shield with its frontal head motif upon the thunderbolt; the shield here not only represents an emblem of the divine and fiery power of their bearers, but must also be interpreted as a predictive artefact for its owner. In Decius Mus Addressing the Legions, which is a small sketch or modello for the larger composition in the Liechtenstein Museum,68 Rubens chose to depict the moment in which Decius Mus is standing on a pedestal before his army and he is describing his dream (fig. 6).

Fig. 6 

Peter Paul Rubens, Decius Mus Addressing the Legions, ca. 1616, oil on hardboard, 80,7 x 84,7 cm, Washington D.C., National Gallery of Art © Samuel H. Kress Collection.

In Roman military contexts divination was a standard practice, as it was seen as a way to interpret the will and favor of the gods. In Rubens’s Decius Mus Addressing the Legions the presence of the eagle on the left in combination with the shield, with its thunderbolt and the flashes on lightning, suggests an association with Roman divinatory rites and with the gift of foresight in particular. In fact, in Greece and Rome the eagle was the bird of divination par excellence, and as a creature of magic it was especially significant in the interpretation of dreams.69 The flight of Jupiter’s most beloved bird offered insight into the god’s designs, and eagle and shield illuminate the hero’s future path. Their prophetic power extends to the helmet showing the legendary founders of Rome, Romulus and Remus raised by the wolf.70 The events that led to the foundation of Rome revolved around two augural rites performed by the two brothers on the Palatine and the Aventine hills; they agreed to entrust the gods with the choice of the site of their new city through the interpretation of an augural response.71 The story of Romulus and Remus represents the most famous example of divination for the history of Rome. On the foundation day of the city the twins took the auspices: they observed the flight of the birds and suddenly Romulus saw the sign of a flying eagle accompanied by a peal of thunder in the left-hand part of the sky (partibus caeli sinistris).72 The birds, but especially lightning and thunder (signa ex caelo), were considered favorable signs from the gods for the recognition of any kingship. In Rubens’s Decius Mus Addressing the Legions, the flying eagle upon the shield adorned with a human head and Jupiter’s thunderbolt is, again, a pictorial translation of a literary passage.73 In this context, the bird and the shield with its thunderbolt, with their prophetic character, may be interpreted as good omens of the hero’s future glory.

Rubens’s Natural Philosophy as a Source of Artistic Invention

The stories of Decius Mus and Achilles raise questions about man’s participation in the workings of divine power, God’s foreknowledge, and the possibility of interpreting the thoughts of the gods to follow a predetermined path. These themes had always been popular subjects for intellectual inquiry and philosophical debate from the earliest times. The Stoics believed that only the gods possessed the knowledge of the future; they believed that the world was ruled by necessity and strict causality, yet on the other hand Stoics recognized man’s free will.74 They held that only a wise man – defined as one who follows the divine plan – is truly free and capable ‘to live according to nature’, and that the chains of events determined by fate were at the same time an expression of the ultimate divine goal (telos).75 Living according to nature means to have ‘knowledge of those things that happen naturally’.76 Since the Stoics did not distinguish God from nature, to live in accordance with nature for them meant to live in accordance with God’s will.77 Understanding the mind of God and nature’s workings was necessary to achieve virtue. But how could man perform actions that are morally good, in imitation of God’s wisdom? In order to practice a full imitatio Dei, one had to acquire knowledge about the natural world by means of divination. The early Stoics endorsed divinatory activities as instruments to attain foresight and knowledge of future events.78 By interpreting the mind of the gods, man was able to approach divine power.79 This reason made divination highly valued among ancient authorities: not only the Stoics, but also Pythagoras, Plato, and the Neoplatonists took a serious interest in divination as the only means to discern the benevolence of the gods.80 Iamblichus, for instance, claims that Pythagoras created a new, numerical form of divination and divine worship: ‘Foreknowledge through numbers, believing this to be purer, more divine, and more suitable to the heavenly number of the gods.’81

At this point, numbers are particularly relevant when dealing with the keystone of Rubens’s portico of his house in Antwerp (fig. 7). Both the shield motif discussed here and the keystone of Rubens’s portico share similar features: a mascaron, with its mouth slightly open, flashes of lightning and a whirlpool of fire that, in the case of the keystone, only flows downwards, narrowing into a wedge-shaped vortex. These correspondences seem to be strengthened by the fact that the portico was completed between 1616 and 1621, the same years in which the motif of the Medusa head with Jupiter’s thunderbolt appears in Rubens’s paintings.82 In the catalogue of the exhibition Palazzo Rubens, this carved stone has been merely described as a ‘Medusa’, but as we have seen, the motif is related to the king of the gods and to creation.83 The keystone’s symbolism was deeply ambiguous, which was probably Rubens’s intention. Gorgons’ heads were placed at doors and other liminal sites and were considered powerful apotropaia, but this Gorgon, in contrast with the classical iconography of Medusa, presents seven flashes of lightning and a fiery vortex. These elements in particular suggest an association with Rubens’s motif on the shields. It is also interesting that in this case Rubens added a numeric component: three jagged flashes of lightning appear in the upper part, one pointing in the direction of the head while the other two proceed at right angles from either side. Four more flashes of lightning shoot through the opening below, accompanying the whirlpool of fire. The number seven has particular significance. Rubens might have employed this number – and its division into three plus four – to convey specific meanings by alluding to the seven planets which move periodically within the zodiac, the seven divinities, the seven days of creation, the first principles of Pythagorean and Hermetic philosophy, the divine names or emanations of the Cabala (sefirot),84 or even the Paracelsian system (tria prima plus four elements) through which the Swiss alchemist described God’s creation of the world.85

Fig. 7 

Keystone of the Portico of the Rubens House, ca. 1616–1621 © Collectie Stad Antwerpen, Rubenshuis, Bart Huysmans and Michel Wuyts.

It is certain that Rubens placed considerable emphasis on the meaning and function of numbers. In his Theoretical notebook the painter-humanist devoted a section – which might have been initially intended as a chapter of the unpublished manuscript – to Pythagorean number symbolism, claiming that not only philosophers but also poets held numbers in great esteem.86 He also stressed that certain numbers contain a hidden law of nature (occultam naturae legem) and therefore are more suitable to honor the gods.87 It is in this context that we should interpret the presence of the seven flashes of lightning, and their division into the upper and lower parts, that accompany the mascaron/Gorgon of the keystone. The first flash of lightning coming from above – probably a reference to celestial fire from the heavens (aether) – points the viewer to the head, the place of wisdom, and might be related to Rubens’s notion of the number one in his Theoretical notebook: ‘It is with reason that Pythagoras calls this number (one) the mind (mens) and the likeness (similitudo) of God.’88 Rubens thus participated in the well-established Hermetic tradition of conveying meaning through numbers. Knowledge of numbers was believed to be necessary for understanding the sacred mysteries of God and nature. Because of their emphasis on numbers the Pythagoreans were claimed as allies by cabalists.89 In addition, Pythagoras’s image as a Greek disciple of Moses facilitated the assimilation of Pythagoreanism into the Cabala.90 Pythagorean number symbolism was further employed to uncover meaning in the book of Genesis, to interpret the other Scriptures, and especially to reveal Christian truths by means of corroborative evidence from other ancient doctrines.91

At this point we should direct our attention to Lipsius’s work on natural philosophy. Rubens scholars have convincingly shown the important influence of Lipsius on the artist’s intellectual and moral agency.92 It is therefore not surprising that the philosopher’s ideas on God and nature, developed in his Physiologia Stoicorum, made their mark on Rubens’s creativity, shaping his artistic production. Relying on the prisca theologia belief and on an eclectic method of approaching the study of the natural world, advocated by Seneca, Lipsius addresses important questions on the nature of God and the human soul in his writings.93 In doing so, he did not revive ancient Stoicism in its classical form, but rather transformed it into a Platonizing interpretation of Seneca’s Stoicism, with the main purpose to find concordances with the Christian religion.94 In his efforts to demonstrate the compatibility between Christianity and Stoic physics, Lipsius was careful to distance himself from some materialistic assertions of the early Stoics. For instance, he rejected the Stoics’ view on the existence of a corporeal God, and established God’s identification with an incorporeal substance, which he identified with the mind or intellect (mens) of the universe, but also with the spiritus or animus of the world.95 Quoting Seneca, but coloring his passages by recurring to Platonic doctrines, Lipsius maintains that God is equal to the ‘universal nature’, a divine principle endowed with reason and knowledge.

He continues his discussion on the substance of God by arguing that not only the Stoics but also other ancient philosophers used to describe God as ‘an eternal fire which envelops and circulates’, a notion extended to the heavenly bodies and the aether.96 This fire of celestial nature is endowed with seminal reason-principles (logoi spermatikoi) and responsible for divine providence. For Lipsius, everything that partakes of ethereal fire is divine, so the stars and the sun, which are formed of it, are themselves gods.97 He also knows that Homer spoke of divine fire. Quoting the famous passage of the Hippocratic treatise De carnibus, Lipsius observes that its author held this fire to be sentient and intelligent, eternal, and possessing knowledge of future events.98 The Flemish philosopher quotes several classical sources to prove that the Stoic God is the ‘artful creative fire’ (ignis artificiosus), a fire endowed with reason and art to create and maintain the universe.99 He then argues that, according to the early Stoics, this divine and intelligent fire is called Jupiter, the king of gods and the sky and the wielder of the thunderbolt.100 Further on, he gives examples of both Hebrews and Christians speaking of God in terms of the imagery of fire and light: God’s appearance to Moses in the burning bush101 and to the Hebrews as ‘a column of fire’102, while Christ is called the ‘Lucidum verbum’, the word of Light.103 Drawing on the Corpus hermeticum and on Neoplatonic sources, Lipsius shows that God is immanent in the universe (cosmos) and that both possess a sentient nature and a perfect reason. This view in which God is the spiritus or animus of the world, the fiery spirit that pervades, knows, and governs everything, constitutes one of the philosopher’s efforts to reconcile Stoicism with Christianity.

According to Diogenes Laërtius, the Stoics thought the cosmos – also referred to as the heavens – to be eternal but subject to periodic cycles of generation and destruction.104 Each cycle of the universe is defined and concluded by the ecpyrosis (the periodic destruction of the cosmos through fire), from which a new generative cycle starts. Ecpyrosis occurs at the end of each cosmic cycle and designates the beginning of the next. For this reason, the Stoics equated ecpyrosis with natural change.105 Ancient sources, including the Stoic writers as well as Aristotle, attributed to Heraclitus a world that was periodically destroyed by fire and then reborn.106 The idea of an eternal world is supported by the principle of transformation of matter, a principle expressed succinctly in the single word ‘mutability’.107 In this view of the world, the transformations of matter through its cyclical pattern of generation and corruption represent the very essence of nature. Without transformation the created world would not exist.108 God is thus seen as a rational being who transforms himself into the cosmos, and these natural changes produced by him are seen as ‘an omnipresent instantiation of his providence’.109

According to the Stoics, there exists an everlasting succession of worlds that manifest exactly the same order; this was believed to be proof of God’s providence, since God knows from the past experiences of previous worlds all that will happen in subsequent worlds. The changes both wrought and symbolized by fire govern the world. Lipsius saw these ideas as supporting the doctrine of divine providence, in which the fiery substance of the heavens, containing the seeds of fate, was also responsible for the lives of everything existing on earth.110 The Stoic concept of ecpyrosis or final conflagration also influenced Christian apocalyptic imagery and eschatological teachings. Early Christian authors attempted to connect the Stoic doctrine of ecpyrosis with the Biblical concept of the end of the world (eschaton),111 but also with the first act of creation described in the first chapter of Genesis (fig. 8).112 At the time of the eschaton, when God shall turn into an eschatological judge and heaven and earth will be destroyed by fire, his glory will fill the all cosmos.113

Fig. 8 

Matthias Gerung, John receives and eats the Book (Rev. 10:8–10), ca. 1530–1531, miniature from the Ottheinrich Bible, Bavaria-Ingolstadt, 1430–1531 © Bayerische Staatsbibliothek München, Cgm 8010 (8, fol. 293r).

Inspired by Lipsius’s views and by the representations of the angel of Revelation – described as holding the seven stars in his right hand, with a face imitating the brilliance of the sun at its brightest – in printed Bibles from the late fifteenth century, Rubens created the seemingly bizarre creature of the keystone.114 Such ideas circulated inside the artist’s workshop as well. In fact, Rubens’s pupils would come to know the emblematic significance of Rubens’s portico. In his magnificent depiction of this wonderful piece of architecture, Jacob Jordaens introduces a little cupid underneath its central arch (fig. 9).115 This putto imitates the gesture of Michelangelo’s Christ in the Last Judgement (fig. 10).116 He is surrounded by clouds – probably a symbol of divine epiphany – and crowned with flowers. Jordaens’s depiction of this child figure signifies that the keystone not only represents the end of time, but also its beginning.117 It is by a spark of light, the first impulse or emanation, that God created the universe. The biblical description of God’s act of creation and the eschaton not only recall the Stoic notion of cosmic cycles of world-order, but also correspond with eschatological expressions familiar to Jewish traditions.118 In the Zohar, also known as the Book of Splendor, a cabalistic treatise from the end of the thirteenth century, the first chapter of Genesis describes the creation of Elohim – one of the names of God in the Hebrew text – initially as a dark and colorless flame originating from eyn sof, the Infinite, which produces radiant colors as it grows in size.119 In the same text, Ezekiel compares the appearance of the divine presence of YHVH to ‘the appearance of the rainbow in the clouds on a day of rain’. In this book God’s divine manifestation includes all colors of the world, the colors of the sefirot.120 This definition of divinity seems quite appropriate to the house of a painter, which ties in with Rubens’s preoccupation with the artist as creator. The shields and the keystone, with their depiction of the cosmos and its Creator, become objects of divine craftsmanship and cosmic grandeur, believed to contain simulacra deorum or the likeness of the gods. They become intelligible images capable of integrating knowledge, truth, and the idea of the good.

Fig. 9 

Jacob Jordaens, Amor and Psyche, ca. 1640–1645, oil on canvas, transferred to panel, 131 x 127 cm, Madrid © Museo Nacional del Prado.

Fig. 10 

Michelangelo, Last Judgement, Sistine Chapel Ceiling, fresco, 1534–1541, Vatican City, Rome © Musei Vaticani.

The keystone in particular also introduces the Renaissance theme of mimesis, the artistic imitation of nature and the parallelism and mutual relationship between God and the world, and the craftsman and his work.121 Rubens must have regarded the art of painting as guided by a divine breath – which the Platonists called furor – and the painter as able to create, to make, and to imitate analogous universes using the medium of his brush. Inspired by God, the painter sees himself as a ‘creating god’ and a ‘philosopher-artist’,122 generating many worlds through the active exercise of his intellect and senses, and as capable of revealing his divinity in the act of artistic creation. Rubens’s carved stone embodied Lipsius’s idea of a God who is both transcendent and immanent in the universe, who is both the eternal and infinite cause of the world and all existing things, and its manifestation in the physical world. God is the ignis artificiosus, the intelligent, providential and creative fire that transforms and sustains the universe; he is the ‘vital force’ that holds the whole world together and preserves it, and which is contained in the celestial bodies – the sun and other stars – and in the human soul. According to Lipsius, the human soul is derived from fire, and thus from the substance of God.

The notion of human divinity was also Pythagorean, since the Pythagorean doctrine of the immortality of the soul included its ascent to the stars at birth and its descent from them at death. To Pythagoras, who was believed to be a proto-Christian, was attributed the idea of human divinity and the notion that the immortal soul was subjected to reward and punishment.123 Attainment of the heavenly sphere was destined for a few, who would become gods through their deeds and virtue.124 This doctrine was shared by the Cabala. Specifically, the Hekhaloth literature describes the journey of the soul and its ascent through the seven heavens, which are ruled by the archons of the seven planetary spheres.125 In Jewish mysticism, these archons opposing themselves against the liberation of the soul from its earthly chains are the ‘gate-keepers’ placed at both sides of the entrance to the heavens.126 It is in this context that we can understand the situation of the keystone of Rubens’s portico in its central position between the two classical protector deities, Hermes and Athena (Hermathena), and the two inscriptions from Juvenal proclaiming the moral teachings that guide man towards a virtuous life (fig. 11).127 Following Lipsius, Rubens creates a powerful image that conveys philosophical and moral principles, forming the bridge between paganism and Christianity in an eclectic synthesis and with a renewed humanist spirit. Rubens surely wanted to convey various meanings in his representation of God, and his efforts to harmonize and unify different philosophical ideas stemmed from his belief in the ‘ancient theology’ (prisca theologia), a belief he shared with Justus Lipius and other scholars.

Fig. 11 

Portico of the Rubens House, ca. 1616–1621 © Collectie Stad Antwerpen, Rubenshuis, Jan Bossier & Carmien Michels.


Inspired by the classical heritage as well as by Lipsius’s natural philosophy, the pictor doctus Peter Paul Rubens borrowed a motif showing the juxtaposition of the Medusa head on thunderbolt from a sixteenth-century Italian drawing. The anonymous Italian artist, in his turn, got it most likely from an ancient Hellenistic prototype. Fascinated by its peculiar and little-known iconography, Rubens used and re-worked this motif on the basis of textual classical sources. He did not make these changes randomly; on the contrary, he arranged the motif in the form of a star, for instance, echoing literary passages from ancient poems in order to resonate with learned viewers. Rubens’ recourse to ekphrastic writing was principally concerned with understanding those ‘secrets of nature’ which the ancients believed to be contained in classical poems. Both the shield motif discussed here and the keystone of Rubens’s portico reveal the painter’s familiarity with the classical tradition and Lipsius’s natural philosophy.

Following the teachings of Lipsius and some of his contemporaries engaged in natural philosophy, Rubens gave birth to an original invention (based on a Hellenistic motif) meant to convey the ideas on the nature of God and the human soul as they had been developed by Lipsius in his Physiologia Stoicorum. In order to blur the differences between Stoic physics and Christianity, Rubens established concordances with the lore of the Cabala, Pythagorean number mysticism, and Hermeticism. This complex amalgam of diverse sources was the result of an eclectic method of approaching the study of nature and was reminiscent of Lipsius’s scholarly contribution to early modern Stoicism. Rubens was not just an exuberant interpreter and translator of ancient poetry; he was mainly interested in the philosophical messages hidden under the veil of poetic expression. Therefore, we should not solely interpret Rubens’s work in light of the principle ut pictura poesis, but within a broader concept outlined by Giordano Bruno at the end of the sixteenth century, which emphasizes the analogy between painting, poetry, and philosophy. Through his artistic achievements, Rubens clearly participated in this endeavor where arts and sciences coexisted, and where the idea of ‘philosophical painting’ was conceived as the most useful and valuable artistic undertaking.