Caesar had crossed the Rubicon five years earlier, plunging Rome into civil war rather than return home as a civilian. After defeating every opposing army, he was appointed dictator perpetuo in early 44 BC. The Roman historian Titus Livius records three incidents that tipped the conspirators toward action. The first came when the Senate marched to present Caesar with new honors, and he refused to stand to greet them -- a breach of protocol that senators read as contempt for their authority. The second occurred during the festival of Lupercalia, when Mark Antony offered Caesar a royal diadem and Caesar, after some hesitation, declined it. Many suspected the refusal was staged, a test of public opinion about monarchy. The third incident involved tribunes who removed crowns placed on Caesar's statues; Caesar had them stripped of their office. To Romans steeped in the mythology of the Republic's founding -- the overthrow of kings -- these gestures carried unmistakable meaning.

The conspiracy began on the evening of February 22, 44 BC, when Cassius Longinus met his brother-in-law Marcus Brutus. They agreed that something had to be done. Over the following weeks, they recruited carefully, preferring senators near the age of forty -- experienced enough to be credible, young enough to act. They avoided reckless youths and feeble elders. They tested potential recruits with innocent-sounding questions about tyranny and duty. By mid-March, between sixty and eighty men had joined. The sheer number reflected Brutus's conviction that the killing must appear legitimate, an act of the Republic itself rather than a private vendetta. Every additional conspirator increased the risk of discovery, but Brutus believed a handful of assassins would look like murderers while a crowd of senators would look like liberators.

On the morning of March 15, Caesar's wife Calpurnia woke from a nightmare in which she held his bloodied body. She begged him not to go to the Senate. Caesar himself felt unwell, and the soothsayer Spurinna had warned him weeks earlier to beware the Ides of March. He nearly stayed home. But Decimus Brutus -- one of the conspirators and a man Caesar trusted -- arrived at his house and persuaded him that the Senate was preparing to offer him the title of king outside Italy. To miss the session would be an insult. Caesar relented. As he walked through the Forum, the soothsayer Spurinna caught his eye. Caesar reportedly told him the Ides of March had come without incident. Spurinna replied that they had come but had not yet gone.

The Senate was meeting not in the Forum but in the Curia of Pompey, inside the Theatre of Pompey, because Caesar's own construction project had closed the regular meeting hall. Decimus Brutus had stationed his personal gladiators in the Theatre's portico -- insurance if something went wrong. When Caesar took his seat, the senator Tillius Cimber approached with a petition on behalf of his exiled brother. He grabbed Caesar's toga and pulled it from his shoulder, the agreed-upon signal. Casca struck first, slashing at Caesar's neck but only grazing him. Caesar caught the blade and cried out. Within moments, the senators closed in from every direction. Cassius slashed his face. Decimus Brutus cut his thigh. Caesar, blinded by blood, stumbled and fell at the base of Pompey's statue. The men kept stabbing until he lay still. Of twenty-three wounds, the physician later found that only the second blow to his chest had been lethal. Caesar died primarily from blood loss.

The conspirators had planned the killing meticulously but had given almost no thought to what came next. They marched to the Capitoline Hill waving bloody daggers, expecting grateful crowds. Instead, Rome fell silent. Citizens barred their doors. When Mark Antony read Caesar's will at the public funeral -- revealing generous bequests to the Roman people and the adoption of Octavian as heir -- the crowd's grief turned to rage. They burned Caesar's body in the Forum and hunted the conspirators through the streets. Within two years, the Liberators' Civil War consumed the Republic. Within two decades, Octavian had become Augustus, the first emperor. The assassination that was meant to preserve republican government had destroyed it. The Theatre of Pompey, where Caesar fell, was eventually buried under centuries of later construction. Today, the site lies beneath a residential neighborhood near the Largo di Torre Argentina, where the ruins of four Republican-era temples mark the general area of the most consequential political murder in Western history.