Julius Caesar, defying the order of the Roman Senate not to so, crosses the Rubicon River with his legion on January 10, 49 BCE famously uttering "alea iacta est" ("the die is cast") and leading to the Roman Civil War.
The Rubicon, a small river in northern Italy, served as the boundary between Caesar's province and Italy proper. His crossing precipitated a civil war, leading to Caesar's rise as dictator and ultimately the end of the Roman Republic, ushering in the Roman Empire. Caesar was assassinated on March 15, 44 BC. "Crossing the Rubicon" now is use to mean "Passing a point of no return".