Wikipedia gives the following information on the search “Crossing the Rubicon”

Julius Caesar's crossing the Rubicon river was an event in 49 BC that precipitated the Roman Civil War, which ultimately led to Caesar's becoming dictator for life and the rise of the imperial era of Rome. Caesar had been appointed to a governorship over a region that ranged from southern Gaul to Illyricum (but not Italy). As his term of governorship ended, the Roman Senate ordered Caesar to disband his army and return to Rome. He was explicitly ordered not to bring his army across the Rubicon river, which was at that time a northern boundary of Italy. In January of 49 BC, Caesar brought the 13th legion across the river, which the Roman government considered insurrection, treason, and a declaration of war, on the Roman Senate. According to some authors, he is said to have uttered the phrase "alea iacta est" — the die is cast — as his army marched through the shallow river.

Today, the phrase "crossing the Rubicon" is an idiom that means "to pass a point of no return".

Historically it refers to the act of Julius Caesar crossing the river in 49 BC that led to establishment of imperial Rome. Idiomatically it means to pass a point of no return.

My question is “When did the idiomatic use of this phrase start and come into common usage?”

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    Until a couple of generations ago, studies of ancient Greek and Roman culture and history played a much more central role in general education than they do now, and the speech of educated people was consequently full of references to it (as they could assume that all other educated people would immediately 'get' the reference). 'Crossing the Rubicon' is merely one of many such references. The phenomenon is not specific to English language; versions of 'crossing the Rubicon' can be found in other languages. – jsw29 Nov 1 '18 at 16:31
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    Also, from en.wiktionary.org/wiki/the_die_is_cast#Etymology "The form “the die is cast” is from the Latin iacta ālea est, a grammatically incorrect translation by Suetonius, 121 CE,[1] of the Ancient Greek phrase of Menander ἀνερρίφθω κύβος (anerrhíphthō kúbos), which Caesar quoted in Greek (not Latin). The Greek translates rather as “let the die be cast!”, or “let the game be ventured!”." – Mark Hubbard Nov 1 '18 at 16:37
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    A Google Ngram of British English shows usage from 1751-1756, but others suggest it was used in the 1600s. – Mark Hubbard Nov 1 '18 at 16:43
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    @MarkHubbard Caesar was Julius's family name. Succeeding Roman emperors used it as a title in honour of him, and could be referred to thus in their own lifetime, but from a historical viewpoint 'Caesar' is C. Julius Caesar. – Kate Bunting Nov 2 '18 at 9:45
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    @MarkHubbard: His name was actually Gaius Julius Caesar, so the Wikipedia author is entirely correct. His adopted son Gaius Julius Caesar Octavianus took the name Augustus Caesar on becoming the first Emperor: the remainder of the Julio-Claudian dynasty continued the use of the family name: and succeeding dynasties and other monarchies who wanted to suggest legimate descent from the Roman Emperors (down to Kaiser Wilhelm II) adopted the style. – TimLymington Nov 2 '18 at 9:45

The following sources suggest that the expressionn entered the English language in the early 17th century:

From the American Heritage Dictionary - Cross the Rubicon:

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. Recounted in Plutarch's Lives: Julius Caesar (c. a.d. 110), the crossing gave rise to the figurative English usage by the early 1600s.

From Etymonline: Rubicon:

in phrase to cross (or pass) the Rubicon "take a decisive step," 1620s.

From Merriam-Webster Rubicon:

Rubicon has been used in English as the name of a significant figurative boundary since at least the early 1600s.


It's not the entire expression, but the earliest example given by the OED is from 1613, where "Rubicon" refers to "a course of events to which one is irrevocably committed after passing a point of no return":

He hath passed his commission (as Caesar did,) and is waded vp to the chinne through the bloudie Rubicon, and so is become Rebell to his Soueraigne Lord the Emperour, as also to the state of the Church.
Aphorismes Ciuill & Militarie

Other early examples use the phrase "pass the Rubicon".

If you wil couragiouslie resolve to cut this Gordion knot with Alexander, and to passe this Rubicon with Cæsar, you shall then trulie and tryumphantlie participate of the ones Fame, and of the others Glorie.
Votivæ Angliæ, 1624

Queen Dido did never more importune Æneas's stay at Carthage, than his mother and sister do his continuance here at London... But now he is past the Rubicon.
The court and times of Charles the First, 1626 (modernized text)

The OED gives several other examples from later in the 1600's, which indicates to me that had to be at least somewhat common at that time.

Apparently the French passer le Rubicon predates the usage in English, since it can be found in Cotgrave's 1611 French/English Dictionary.

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