Septimius had served under Pompey in his war against the pirates in 67 BC, and he was in the army with which Aulus Gabinius restored Cleopatra's father Ptolemy XII Auletes to the throne in 55 BC. He had stayed in Egypt as part of a garrison, known as the Gabiniani, to support the king. In Commentarii de Bello Civili, Caesar refers to him as a "military tribune".
Septimius was a leading figure among the Gabiniani. When Pompey fled to Egypt in 48 BC following his defeat by Julius Caesar at the Battle of Pharsalia, he hoped to gain their support along with that of the new Egyptian king Ptolemy XIII, having been friends with Egypt's prior king, Ptolemy XII Auletes; however the advisers of the child successor believed they could win Caesar's favor by killing his foe. The Egyptian general Achillas met Pompey at the shore in Alexandria accompanied by Septimius and a centurian named Salvius. They greeted him under a pretense of friendship and killed him upon the landing.
According to both Plutarch's and Caesar's account, Pompey was reassured by the presence of Septimius, whom he knew from earlier campaigns. But it was Septimius who led the attack by stabbing Pompey in the back, then Salvius and Achillas joined in. Septimius then beheaded the corpse and removed Pompey's signet ring. The killing did not placate Caesar and in the ensuing war the Gabiniani sided with Cleopatra's brother Ptolemy XIII, against Caesar and Cleopatra. The fate of Septimius is not recorded.
Later literary accounts often attributed Pompey's murder solely to Septimius, or place the principal guilt on him. This is the case in the poem Pharsalia by the Roman poet Lucan, in which the fact that Septimius, a Roman, was doing the bidding of a foreign king is depicted as especially shameful. Lucan portrays Septimius as the archetype of a traitor: "With what reputation will posterity send Septimius into the centuries? What name will this wickedness have from those who call what Brutus did a crime?".
In the Massinger and Fletcher play The False One (c.1620), Septimius is the central character, the "false one" of the title. He also appears in Pierre Corneille's La Mort de Pompée (1643). In 1910, John Masefield treated Pompey and Septimius in his The Tragedy of Pompey the Great. He also appears in the George Bernard Shaw play Caesar and Cleopatra (1898), and the HBO television series Rome (depicted in the episodes "Pharsalus" and "Caesarion"). In Shaw's play Caesar forgives him, in Rome Caesar orders his execution.
- Beryl Rawson, The Politics of Friendship: Pompey and Cicero Volume: 6. Sydney University Press. 1978, p.177
- Maspero, pp. 316-19.
- Plutarch, Life of Pompey
- S. H. Braund (trans), Lucan, Pharsalia, book 8, 610.
- Eugene M. Waith, "The Death of Pompey: English Style, French Style," in: Shakespeare and Dramatic Tradition, William R. Elton and William B. Long, eds., Newark, DE, University of Delaware Press, 1989; pp. 276–85.
- Maspero, Gaston, et al. History of Egypt, Chaldea, Syria, Babylonia, and Assyria. Translated by M. L McClure and Herbert McClure. The Grolier Society, 1904.
- Plutarch, The Life of Pompey.