Italy (WHTM) — 2072 years later, it’s an idiom that’s still in use.

“Crossing the Rubicon” has come to mean taking a course of action from which there is no turning back. It’s an early version of “what’s done is done” or “passing the point of no return.” But “crossing the Rubicon” implies a really risky, dangerous choice that could have dire consequences for the person who makes that decision.

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So, what is a Rubicon and why is crossing it an act fraught with peril?

Well, the Rubicon is a small, shallow river located in northeastern Italy. It starts in the Apennine Mountains, and flows to the Adriatic Sea, passing between the towns of Rimini and Casena along the way. The name Rubicon derives from the Latin word “rubeus” or “red,” due to iron deposits in the area that give the water a reddish hue.

In the era of the Roman Republic, the river was a boundary. In fact, it was the extreme northern border of Italy. North of the river was Cisalpine Gaul, a Roman province.

As for who “crossed the Rubicon,” that would be Julius Ceasar, one of the most famous and most mispronounced names in history. Gaius Julius Caesar (pronounced roughly as GAH-ee-oos YOO-lee-oos KUY-sahr) was born around 100 B.C.E., about the same time the Roman Republic was starting to come apart at the seams. By the time he was in his 20s, he’d already been on the losing side of one civil war. He joined the army and built a reputation as a military leader.

Jump cut past a lot of important stuff, and in 59 B.C.E. he was a consul in Rome, forming an alliance with Gnaeus Pompeius Magnus (Pompey the Great) and Marcus Licinius Crassus which became known as the First Triumvirate. The Triumvirate controlled Rome, and Caesar became Governor of Gaul (north-central Europe), which required a large army to keep the Gauls under Roman control. (Caesar wrote a book about his exploits, Commentary on the Gallic Wars, which is still studied today-though usually in translation.)

But Caesar’s successes in Gaul strained relations with Pompey and Crassus. When Crassus died in 53 B.C.E., Pompey sided with Caesar’s opponents-of which there were many in the Roman Senate. Caesar was ordered to return to Rome, and leave his army in Gaul. Caesar returned- but brought his army with him. On January 10, 49 B.C.E. he and his troops crossed the Rubicon. In doing so he violated the laws concerning his military authority (his imperium) triggering a Civil War. Supposedly when Caesar crossed the river, he stated “Alea iacta est” (“The die is cast”)

The civil war was brief and ended badly for Caesar’s opponents. (Pompey was killed in Eqypt on orders of Pharaoh Ptolemy VIII to curry favor with Caesar.) In 46 B.C.E. Julius Caesar was made Dictator of Rome for ten years. In 44 B.C.E. he declared himself dictator for life. (This ended up not being a good idea.)

Oddly enough, for a long time, the Rubicon River was lost in plain sight. With the fall of the Western Roman Empire, repeated floodings, changes in the river’s course, and various civil engineering projects, people lost track of which of the rivers in the area was THE Rubicon. In fact, for many years it was known as the Fiumicino River. It wasn’t until the 20th century that enough old records were found, cross-referenced, and compared to modern topography that it was established that the Rubicon was the Rubicon. (And there are still people who have their doubts.)

So if you visit Italy today, it is possible for you to cross the Rubicon, though nobody knows precisely where Julius Caesar acted on his fateful decision.

At least you won’t have to worry about triggering a civil war…