My subtitle promises pedantry, so here goes:

Every educated person knows that Caesar said alea iacta est, "the die is cast", when he crossed the Rubicon. 'Jane Galt' (Asymmetrical Information), PejmanPundit, and Colby Cosh have all quoted it recently in reference to Bush's speech yesterday.

The source of the famous quotation is Suetonius' Lives of the Twelve Caesars, Book I (Divus Iulius), chapter 32. The last I heard, no one had been able to determine which of several small rivers south of Ravenna is the ancient Rubicon, but whichever it was was the border between Italy and the provinces: the Po Valley was still considered part of Gaul. Caesar could not legally bring his army into Italy, but he did not feel safe returning to Rome from the conquest of Gaul without it. Crossing the river with his army constituted a declaration of civil war.

In fact, he almost certainly said alea iacta esto, "let the die have been cast", not a statement of fact but a command, specifically a perfect imperative. Something very like a perfect imperative in English would be "have this done by Monday". It's a command, but with the idea of completion in it. In Caesar's case, completion means irrevocability.

The emendation was made by Erasmus, and was reargued by Robert Renehan in 1969 (Greek Textual Criticism: A Reader, 54-55). As he says, "the rare perfect imperative corrupted to a familiar perfect indicative" is "a trivialization of the commonest sort". (He also says "the general reluctance of editors of Suetonius to this day to print esto is incomprehensible to me". To me, too.) The main point in favor of esto is that Caesar was quoting a well-known Greek proverb which uses a perfect imperative. He most likely said it in Greek, anyway. Plutarch reports (Life of Pompey 60, Life of Caesar 32) that he said it before he crossed the river, and the proverb was a favorite of those about to embark on a risky undertaking. If anyone is wondering, the Greek is anerrhíphthw kúbos (with the W representing long O, that is, omega).

Of course, as I write in the two-day interval between Bush's speech and (we all assume) Gulf War II, alea iacta esto is the more appropriate reading: let's get this over with.