This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed.Find sources: "Crossing the Rubicon" – news · newspapers · books · scholar · JSTOR (May 2015) (Learn how and when to remove this message)
The modern Rubicon river (dark blue), believed to be the same river crossed by Caesar

The phrase "crossing the Rubicon" is an idiom that means "passing a point of no return".[1] Its meaning comes from allusion to the crossing of the river Rubicon by Julius Caesar in early January 49 BC. The exact date is unknown.[2] Scholars usually place it on the night of 10 and 11 January because of the speeds at which messengers could travel at that time.[3] It is often asserted that Caesar's crossing of the river precipitated Caesar's civil war;[4] however, Caesar's forces had already crossed into Italy and occupied Ariminum the previous day.[5]

The civil war ultimately led to Caesar's becoming dictator for life (dictator perpetuo). Caesar had been appointed to a governorship over a region that ranged from southern Gaul to Illyricum. As his term of governorship ended, the Senate ordered him to disband his army and return to Rome. As it was illegal to bring armies into Italy (the northern border of which was marked by the river Rubicon) his crossing the river under arms amounted to insurrection, treason, and a declaration of war on the state. According to some authors, he uttered the phrase alea iacta est ("the die is cast") before crossing.


During the late Roman Republic, the river Rubicon marked the boundary between the Roman province of Cisalpine Gaul to the northeast and Italy proper (controlled directly by Rome and its allies) to the south. On the northwestern side, the border was marked by the river Arno, a much wider and more important waterway, which flows westward from the Apennine Mountains (its source is not far from the Rubicon's source) into the Tyrrhenian Sea.

Governors of Roman provinces were appointed promagistrates with imperium (roughly, "right to command") in one or more provinces. The governors then served as generals of the Roman army within the territory they ruled. Roman law specified that only the elected magistrates (consuls and praetors) could hold imperium within Italy. Any magistrate who entered Italy at the head of his troops forfeited his imperium and was therefore no longer legally allowed to command troops.

Exercising imperium when forbidden by the law was a capital offense. Furthermore, obeying the commands of a general who did not legally possess imperium was a capital offense. If a general entered Italy in command of an army, both the general and his soldiers became outlaws and were automatically condemned to death. Generals were thus obliged to disband their armies before entering Italy.

Julius Caesar

Julius Caesar, depicted as pausing on the banks of the Rubicon

In January 49 BC, Gaius Julius Caesar led a single legion, Legio XIII, south over the Rubicon from Cisalpine Gaul to Italy to make his way to Rome. In doing so, he deliberately broke the law on imperium and made armed conflict inevitable. Roman historian Suetonius depicts Caesar as undecided as he approached the river and attributes the crossing to a supernatural apparition. It was reported that Caesar dined with Sallust, Hirtius, Oppius, Lucius Balbus and Sulpicus Rufus on the night after his famous crossing into Italy on 10 January.[6] A dramatic moment in literary narratives, the importance of the anecdote is undermined somewhat by Caesar's forces having already crossed into Italy the previous day. By the time Caesar himself entered Italy the war had already begun, with his legate, Quintus Hortensius, occupying the Italian town of Ariminum.[7]

According to Suetonius, Caesar uttered the famous phrase ālea iacta est ("the die has been cast").[8] The phrase "crossing the Rubicon" has survived to refer to any individual or group committing itself to a risky or revolutionary course of action, similar to the modern phrase "passing the point of no return". Caesar's decision for swift action forced Pompey, the consuls, and a large part of the Roman Senate to flee Rome.



  1. ^ Beard 2015, p. 286.
  2. ^ Beard 2015, p. 286. "Sometime around 10 January 49 BCE, Julius Caesar... crossed the Rubicon... the exact date is not known, nor even the location of this most historically significant of rivers".
  3. ^ Morstein-Marx 2021, p. 322.
  4. ^ Eg Redonet, Fernando Lillo (2017-03-15). "How Julius Caesar Started a Big War by Crossing a Small Stream". History. National Geographic. Archived from the original on April 10, 2021. Retrieved 2023-11-21.
  5. ^ Badian 1990, p. 30. "The civil war did not begin with Caesar's crossing of the Rubicon. By the time he reached the river, Q. Hortensius had already occupied Ariminum".
  6. ^ Dando-Collins, Stephan (2002). The Epic Saga of Julius Caesars Tenth Legion and Rome. p. 67. ISBN 0-471-09570-2.
  7. ^ Badian 1990, pp. 29–30.
  8. ^ Lives of the Caesars, "Divus Julius" sect. 32. Suetonius gives the Latin version, iacta alea est, although according to Plutarch's Parallel Lives, Caesar quoted a line from the playwright Menander: "ἀνερρίφθω κύβος", anerríphthō kȳbos, "let the die be cast". Suetonius' subtly different translation is often also quoted as alea iacta est. Alea was a game played with a die or dice rather than the actual dice themselves, so another translation might be "The game is afoot."


44°05′35″N 12°23′46″E / 44.093°N 12.396°E / 44.093; 12.396