Die is cast

As in 'the die is cast', meaning that a crucial and probably irreversible decision has been taken. The most obvious derivation is from the throw or cast of a single die (dice being the plural of die). Once the die is thrown, the result is there for all to see and it cannot be reversed. Julius Caesar is thought to have said something similar, but obviously in Latin, “iacta alea est”, when he crossed the Rubicon in 49 BC and there was no turning back from his collision course with the Roman Senate. See also Straight as a die