In 49 BCE Caesar crossed the Rubicon with his army, breaking the basic Roman prohibition against bringing legions into Italy. Over the next four years he defeated his rival Pompey in Greece and the Pompeian factions in Egypt, Africa and Spain. In February 44 BCE the Senate granted him the title dictator perpetuo — dictator for life — an open transgression of the magistracy limits that lay at the heart of Roman political culture.

Within the Senate a conspiracy took shape, including many former Pompeians whom Caesar had personally pardoned — Marcus Brutus and Cassius among them. On 15 March Caesar entered the Senate session being held in the curia attached to the Theatre of Pompey and was surrounded by roughly 60 senators. Ancient sources (Suetonius, Plutarch, Appian) report 23 stab wounds. The line 'Et tu, Brute?' belongs to Shakespeare; Suetonius reports a Greek phrase, 'kai sy, teknon' ('you too, child?'), whose authenticity is itself uncertain.

The conspirators intended to restore the Republic; in practice they accomplished the opposite. Mark Antony and Caesar's adopted heir Octavian rode the wave of public anger, hunted the assassins down, and defeated them at Philippi in 42 BCE. The decade of power struggle that followed ended with Octavian's victory over Antony at Actium in 31 BCE. In 27 BCE Octavian, now bearing the title Augustus, became the first Roman emperor.

The symbolic weight loaded onto the Ides of March exceeds the event itself. The Roman Republic had been mired for decades in civil war, proscription and oligarchic deadlock; Caesar's death did not resolve that crisis, it merely wrote its final page. Yet in European political imagination the scene cast the mould of 'tyrannicide' — a reference reached for again and again from the Renaissance to the modern revolutions.