The battle between Hercules and Cacus is a major episode in Aeneid Book 8 alongside the meeting between Aeneas and Evander and the description of the Shield of Aeneas. Toward the end, when Hercules opens Cacus’ cave, Virgil makes reference to the conflict between light and darkness, and to the fear felt by Cacus when he sees that there is no way out (8.241–53):
But Cacus’ lair and his vast palace appeared, and its shadowy caverns lay open deep within, just as if the earth, split deep by some force, should unlock the infernal seats and unbar the pallid realms hateful to the gods, and the vastness of the depths should be seen from above, and the shades should tremble at the invading light. With arrows from above Alcides presses him as he is caught suddenly by the unexpected light, shut in by hollow rock, and roaring unnatural sounds. Alcides calls upon all his weapons, and threatens him with branches and huge millstones. He, however—for now no other escape from the danger remained—spews forth a vast amount of smoke from his jaws—amazing in the telling—and covers his home in blinding fog …Footnote 1
Trapped and attacked by Hercules, Cacus expels a great cloud of smoke from his throat, which Virgil describes as wondrous to tell. If we look at lines 246–9, I think that further conclusions might be drawn:
The last letters of these lines form the telestich sēma , a Greek word which bears a range of meanings, including ‘sign’, ‘omen’, ‘portent’ or ‘tomb’. The potentially accidental occurrence of acrostics and telestichs, especially short ones,Footnote 2 is a reason for caution and has spurred much debate in recent decades.Footnote 3 In my view, however, this telestich is not accidental, since it fits the scene of the battle between hero and monster. The vocabulary used by Virgil is significant here.
As the light enters the cave, Cacus’ den is revealed by Hercules. Virgil seems to insist on a lexicon related to the fields of vision, light and revelation (for example 241 apparuit; 242 patuere; 246 cernatur, lumine; 247 insperata luce), which are clearly connected to the ideas conveyed by the term σῆμα (and by the related verb σημαίνω),Footnote 4 which conveys ideas of signs and revealing. The darkness of the cave is disturbed by the light that enters and reveals Cacus, and Virgil compares it to the underworld and Cacus to the Manes (who provide the first letter to the telestich at line 246) who would tremble at this sudden intrusion of the light of day. One must also note that line 246, the first of the telestich, opens with cernatur, thus reinforcing the meaning of σῆμα, in the telestich. However, this play between light and darkness/underworld might lead us to think that Virgil is playing with the polysemy of σῆμα, and nodding also to its meaning ‘tomb’. Scholarship has shown that σῆμα was used in this sense by the Augustan poets. Mitchell has pointed to possible telestichs of sēma elsewhere in the Aeneid (9.270–3, relating to Ascanius and Nisus),Footnote 5 in Hor. Carm. 2.3.13–16 as well as in Ov. Her. 2.136–9 and 6.106–9, with the meaning of ‘tomb’.Footnote 6 In Aen. 8.246–9, where Cacus is about to die, this wordplay may also signify to Virgil's original audience that the revelation of Cacus’ home turns it into his tomb. In doing so, the poet aligns himself with an established literary tradition.Footnote 7
Regarding the meaning of sēma as ‘wonder’ and/or ‘prodigy’, one should also pay attention to the clause mirabile dictu (252), used of Cacus expelling smoke in desperation.Footnote 8 Virgil is fond of this expression, and he used it eight times in discussing wondrous things, such as the grafting technique in G. 2.30–1 quin et caudicibus sectis mirabile dictu | truditur e sicco radix oleagina ligno,Footnote 9 mares conceiving to the wind in G. 3.274–5 exceptantque leuis auras, et saepe sine ullis | coniugiis uento grauidae mirabile dictu,Footnote 10 and in connection to Fama in Aen. 4.182.Footnote 11 Fratantuono and Smith describe the faucibus ingentem fumum (mirabile dictu) of Aen. 8.252 as ‘a note of particularly magical, supernatural force’.Footnote 12 The sense of the telestich is therefore coherent with the context, as Fowler previously noted for the famous Mars acrostic in the Aeneid.Footnote 13
Considering the above, it seems to me that the telestich sēma in Aen. 8.246–9 should be recognized as intentional. It runs to only four letters, and one might think it likely accidental for this reason, but the polysemy of the word sēma means it is relevant to the context in the poem in several senses. Virgil's insistence on the semantically related ideas of light, vision and revelation, and his use of the phrase mirabile dictu, typically associated with wonders and prodigia, also strengthen the case for the credibility and the intentional character of this wordplay.