Julius Caesar is set in Rome at the tail end of the Roman Republic, the period in which an early form of representative democracy governed the civilization. The play traces the set of events that will eventually lead to Rome's transition from representative republic into all out empire in the decades following Caesar's death.
The play condenses the historical events of this period into a more manageable timeline for a dramatic narrative. It opens in the weeks preceding Caesar's assassination on March 15 in 44 B.C.E. After Caesar's assassination, Shakespeare also recounts the formation of the "Second Triumvirate" between Antony, Octavius, and Lepidus and their campaign of war against the architects of Caesar's assassination, Brutus and Cassius, which took place from 43 to 42 B.C.E. The war came to a close at the two Battles of Philippi, fought a few weeks apart from each other in October of 42 B.C.E., although Shakespeare portrays the battle as one singular event at the very end of Julius Caesar.
The first four acts of the play take place in and around Rome, with the climactic assassination of Caesar occurring in the Roman Senate. The final act of the play—portraying the Battles of Philippi—takes place on a battlefield in Greece near the city of Philippi.
Aside from the handful of details that Shakespeare adjusts for dramatic effect or the practical considerations of actually staging the show, Julius Caesar is largely accurate to its historical setting. Shakespeare used the biographies of Caesar written by the Greek author Plutarch as a reference.