Why did Rome's own senators murder Julius Caesar?

On 15 March, 44 BC, around sixty Roman senators surrounded Julius Caesar in a Senate meeting and stabbed him. They did it because Caesar, after winning a civil war, had made himself dictator perpetuo, dictator for life, and seemed to many senators to be reaching for the title of king. Ancient historians record a string of incidents that made it worse: Caesar once stayed seated while a Senate delegation came to honor him, he stripped two tribunes of office after they removed a crown placed on his statue, and at a public festival his co-consul Mark Antony twice offered him a diadem in front of a mostly silent crowd.

The plot began quietly in February 44 BC, when Cassius Longinus and his brother-in-law Marcus Brutus agreed something had to be done. They recruited roughly sixty to eighty fellow senators, mostly men around forty years old, debating for weeks over where and how to strike. They finally chose a Senate meeting itself, since only senators were allowed inside and Caesar's usual protective friends could not follow him in. Brutus insisted that only Caesar be killed, not his allies too, so the act would look like removing a tyrant rather than a political purge, and that argument won the others over.

On the day itself, a conspirator grabbed Caesar's toga as a signal, another struck the first blow, and the rest closed in with daggers from every side until Caesar fell near a statue of his old rival Pompey. He was stabbed 23 times, but a later examination, the first recorded autopsy in history, found that only a single wound near his ribs had actually been fatal; he died mostly from blood loss.

The murder did not save the Republic the conspirators claimed to be defending. It triggered a new civil war, led to Caesar being declared a god, and cleared the way for his teenage heir Octavian to rise through the chaos and eventually become Rome's first emperor, Augustus.