structural:expansion, structural:scholar_edition
Forming the alliance

With Antony defeated, the senate assigned command of the legions in northern Italy to Decimus. Sextus Pompey, son of Caesar's old rival Pompey Magnus, was given command of the Republic's fleet from his base in Sicily while Brutus and Cassius were granted the governorships of Macedonia and Syria respectively. These appointments attempted to renew the "republican" cause. However, the eight legions serving under Octavian, composed largely of Caesar's veterans, refused to follow one of Caesar's murderers, allowing Octavian to retain his command. Meanwhile, Antony recovered his position by joining forces with Marcus Aemilius Lepidus, who had been assigned the governorship of Transalpine Gaul and Nearer Spain. Antony sent Lepidus to Rome to broker a conciliation. Though he was an ardent Caesarian, Lepidus had maintained friendly relations with the senate and with Sextus Pompey. His legions, however, quickly joined Antony, giving him control over seventeen legions, the largest army in the West.

By mid-May, Octavian began secret negotiations to form an alliance with Antony to unify the Caesarians against the liberatores. Remaining in Cisalpine Gaul, Octavian dispatched emissaries to Rome in July 43 BC demanding he be appointed consul to succeed Hirtius and Pansa and that the senate rescind the decree declaring Antony a public enemy. When the senate refused, Octavian marched on Rome with his eight legions and assumed control of the city in August 43 BC. Octavian had himself irregularly elected consul with a cousin, rewarded his soldiers, and then set about prosecuting Caesar's murderers. Under the lex Pedia, all of the conspirators and Sextus Pompey were convicted "in absentia" and declared public enemies. Then, at the instigation of Lepidus, Octavian went to Cisalpine Gaul to meet Antony.

In November 43 BC, Octavian, Lepidus, and Antony met near Bononia. After two days of discussions, the group agreed to establish a three man dictatorship to govern the Republic for five years, known to modern historians as the Second Triumvirate. They shared military command of the republic's armies and provinces among themselves: Antony received Gaul, Lepidus Spain, and Octavian (as the junior partner) Africa. They jointly governed Italy. The triumvirate would have to conquer the rest of Rome's holdings; Brutus and Cassius held the Eastern Mediterranean, and Sextus Pompey held the Mediterranean islands. On 27 November 43 BC, the triumvirate was formally established by a new law, the lex Titia. Octavian and Antony reinforced their alliance through Octavian's marriage to Antony's stepdaughter, Claudia.

The primary objective of the triumvirate was to avenge Caesar's death and to make war upon his murderers. Before marching against Brutus and Cassius in the East, the triumvirs issued proscriptions against their enemies in Rome. The dictator Lucius Cornelius Sulla had taken similar action to purge Rome of his opponents in 82 BC. The proscribed were named on public lists, stripped of citizenship, and outlawed. Their wealth and property were confiscated by the state, and rewards were offered to anyone who secured their arrest or death. With such encouragements, the proscription produced deadly results; two thousand equites were executed, and one third of the senate. Antony forced Octavian to give up Cicero, a personal enemy of Antony and friend of Octavian, who was then killed on 7 December. The confiscations helped replenish the state treasury, which had been depleted by Caesar's civil war the decade before; when this seemed insufficient to fund the imminent war against Brutus and Cassius, the triumvirs imposed new taxes, especially on the wealthy. By January 42 BC the proscription had ended; it had lasted two months, and though less bloody than Sulla's, it traumatized Roman society. A number of those named and outlawed had fled to either Sextus Pompey in Sicily or to the liberatores in the East. Senators who swore loyalty to the triumvirate were allowed to keep their positions; on 1 January 42 BC, the senate officially deified Caesar as " The Divine Julius ", and confirmed Antony's position as his high priest.