RUBICON Cross the rubicon: "(ru bi kan) a boundary or limit, which when crossed commits a person irrevocably. In 49 B.C., Julius Caesar led his army to the banks of the Rubicon, a small river that marked the boundary between Italy and Gaul and which the Roman Senate had forbidden him to cross. The die is cast, said Caesar, wading in, knowing full well that this step would mean civil war
" An example: Pat Buchanan, Newsweek, March 1, 1999: "I havent crossed the Rubicon yet. Im up in the trees looking down at the river." From "Merriam-Websters Dictionary of Allusions" by Elizabeth Webber and Mike Feinsilber (Merriam-Webster, Springfield, Mass., 1999).