1
general::
Phrase(s): cross the Rubicon
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.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
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.
American Heritage Idioms