The Battle of Philippi was the final battle in the Wars of the Second Triumvirate between the forces of Mark Antony and Octavian (the Second Triumvirate) and the forces of Julius Caesar's assassins Marcus Junius Brutus and Gaius Cassius Longinus in 42 BC, at Philippi in Macedonia. The Second Triumvirate declared this civil war to avenge Julius Caesar's murder.

The battle consisted of two engagements in the plain west of the ancient city of Philippi. The first occurred on the first week of October; Brutus faced Octavian, while Antony's forces were up against those of Cassius. At first, Brutus pushed back Octavian and entered his legions' camp. But to the south, Cassius was defeated by Antony, and committed suicide after hearing a false report that Brutus had also failed. Brutus rallied Cassius' remaining troops and both sides ordered their army to retreat to their camps with their spoils, and the battle was essentially a draw, but for Cassius' suicide. A second encounter, on 23 October, finished off Brutus's forces, and he committed suicide in turn, leaving the triumvirate in control of the Roman Republic.

Philippi (in Greek Φίλιπποι Philippoi) was a city in eastern Macedonia, established by Philip II in 356 BC and abandoned in the 14th century after the Ottoman conquest. The present municipality Filippoi is located near the ruins of the ancient city and it is part of the region of East Macedonia and Thrace in Greece.

Philippi was established by the king of Macedon, Philip II, on the site of the Thasian colony of Krinides or Crenides (Κρηνἱδες, "Fountains"), near the head of the Aegean Sea at the foot of Mt. Orbelos about 8 miles north-west of Kavalla, on the northern border of the marsh that in Antiquity covered the entire plain separating it from the Pangaion hills to the south of Greece.

The objective of founding the town was to take control of the neighbouring gold mines and to establish a garrison at a strategic passage: the site controlled the route between Amphipolis and Neapolis, part of the great royal route which crosses Macedonia from the east to the west and which was reconstructed later by the Roman Empire as the Via Egnatia. Philip II endowed the new city with important fortifications, which partially blocked the passage between the swamp and Mt. Orbelos, and sent colonists to occupy it. Philip also had the marsh partially drained, as is attested by the writer Theophrastus. Philippi preserved its autonomy within the kingdom of Macedon and had its own political institutions (the Assembly of the demos). The discovery of new gold mines near the city, at Asyla, contributed to the wealth of the kingdom and Philip established a mint there. The city was finally fully integrated into the kingdom under Philip V.

Gaius Julius Caesar (Classical Latin: [ˈɡaː.i.ʊs ˈjuː.lɪ.ʊs ˈkaj.sar], July 100 BC – 15 March 44 BC) was a Roman general and statesman and a distinguished writer of Latin prose. He played a critical role in the gradual transformation of the Roman Republic into the Roman Empire.

In 60 BC, Caesar, Crassus and Pompey formed a political alliance that was to dominate Roman politics for several years. Their attempts to amass power through populist tactics were opposed by the conservative elite within the Roman Senate^{[citation needed]}, among them Cato the Younger with the frequent support of Cicero. Caesar's conquest of Gaul, completed by 51 BC, extended Rome's territory to the English Channel and the Rhine. Caesar became the first Roman general to cross both when he built a bridge across the Rhine and conducted the first invasion of Britain.

These achievements granted him unmatched military power and threatened to eclipse Pompey's standing. The balance of power was further upset by the death of Crassus in 53 BC. Political realignments in Rome finally led to a standoff between Caesar and Pompey, the latter having taken up the cause of the Senate. Ordered by the Senate to stand trial in Rome for various charges, Caesar marched on Rome with one legion—legio XIII—from Gaul to Italy, crossing the Rubicon in 49 BC. This sparked a civil war from which he emerged as the unrivaled leader of the Roman world.