cross the Rubicon, to

To commit to a particular plan or course of action that cannot be reversed. The phrase refers to how Julius Caesar crossed the Rubicon river and became embroiled in civil war in 49 BCE. Look, if you cheat on this test, you are crossing the Rubicon, man. You can't take that back. I think I crossed the Rubicon when I took this management position. It would be a huge pay cut to go back to my old job, and my boss would be furious.

Fig. to do something that inevitably commits one to following a certain course of action. (Alludes to the crossing of the River Rubicon by Julius Caesar with his army, which involved him in a civil war in B.C. 49.) Jane crossed the Rubicon by signing the contract. Find another job before you cross the Rubicon and resign from this one.

Irrevocably commit to a course of action, make a fateful and final decision. For example, Once he submitted his resignation, he had crossed the Rubicon. This phrase alludes to Julius Caesar's crossing the Rubicon River (between Italy and Gaul) in 49 b.c., thereby starting a war against Pompey and the Roman Senate. Recounted in Plutarch's Lives: Julius Caesar (c. a.d. 110), the crossing gave rise to the figurative English usage by the early 1600s.

If you cross the Rubicon, you make an important decision which cannot be changed and which will have very important consequences. Today the Government has crossed the Rubicon in favour of the Euro. In England and Wales the Rubicon has been crossed regarding the charging of fees to students. Note: This expression is variable, for example people sometimes talk about the crossing of the Rubicon or a crossing of the Rubicon. Such a decision would be a crossing of the Rubicon. Note: Sometimes this important decision is referred to as a person's Rubicon. There would be no turning back; if he was making a big mistake, this was his Rubicon. Note: The Rubicon was a small river which separated Roman Italy from Gaul, the province ruled by Julius Caesar. Caesar crossed the Rubicon in 49 BC, invaded Roman Italy, and started a civil war. `The die is cast' is based on the same incident.

To take an irrevocable step. The term dates from 49 b.c., when Julius Caesar crossed this river between Italy and Cisalpine Gaul, thereby invading Italy and disobeying Pompey and the Roman Senate. The Senate, he had learned, intended to disband his army, whereupon Caesar joined his advance guard on the Rubicon’s banks and told them, “We may still draw back, but once across that little bridge we will have to fight it out.” The term has been a cliché since about 1700.