Largo de Torre Argentina
Caesar's death is nearly as legendary as his life. After defeating Pompey and appointing himself Rome's dictator, he continued to consolidate his personal power, angering Romans who felt him a threat to the Republic. When, in 44 B.C., Caesar declared himself dictator for life, factions in the Senate turned against him, deciding that the only way to preserve the Republic was to assassinate Caesar.
As legend has it, Caesar ignored several omens that might have helped him avoid his assassination, including a plea from his wife to remain home on the day of his murder. Ignoring these omens, he went to the Senate, where a group of men, including his friend Brutus, waited for him. In Pompey's Theater, on March 15 44 B.C., the conspirators stabbed Caesar to death.
Pompey's Theater is long gone (ruins have been incorporated into other structures, making it impossible to truly discern which is which) but the busy square Largo de Torre Argentina stands where the theater once was. It wasn't until recently, in 2012, that archaeologists found definitive physical proof, in the form of a concrete structure, that Pompey's Theater did indeed once stand in the square.
To visit the Torre Argentina, head to Rome's Centro Storico (also home to the Pantheon and Campo de' Fiori). The physical remains of ruins inside of the square are off-limits, but can be seen from the square's outskirts.