Ru·​bi·​con ˈrü-bi-ˌkän How to pronounce Rubicon (audio)
: a bounding or limiting line
especially : one that when crossed commits a person irrevocably

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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. Caesar knew Roman law forbade a general from leading his army out of the province to which he was assigned. By crossing the Rubicon, he would violate that law. "The die is cast," he said, wading in. That act of defiance sparked a three-year civil war that ultimately left Julius Caesar the undisputed ruler of the Roman world. It also inspired English speakers to adopt two popular sayings -crossing the Rubicon and the die is cast-centuries later. Rubicon has been used in English as the name of a significant figurative boundary since at least the early 1600s.

Examples of Rubicon in a Sentence

Recent Examples on the Web The Pro Football Hall of Fame passed an uncomfortable Rubicon in 2018 when the former Baltimore Ravens linebacker Ray Lewis spoke for more than 33 minutes at his induction ceremony. Ken Belson, New York Times, 3 Aug. 2023 The widespread assumption was that nuclear weapons were weapons unlike any other, and that using them would mean crossing a Rubicon to Armageddon. Jackson Lears, Harper's Magazine, 9 June 2023 Treasury Secretary Janet Yellen had no more maneuvers to stave off a default that could have hit on Monday – a Rubicon the government has never crossed. Todd J. Gillman, Dallas News, 2 June 2023 The dehumanization of immigrants (or anyone) is a Rubicon that, once crossed, can set in motion the worst of humanitarian disasters. Molly Jong-Fast, Vogue, 23 Sep. 2022

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'Rubicon.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History


Latin Rubicon-, Rubico, river of northern Italy forming part of the boundary between Cisalpine Gaul and Italy whose crossing by Julius Caesar in 49 b.c. was regarded by the Senate as an act of war

First Known Use

1613, in the meaning defined above

Time Traveler
The first known use of Rubicon was in 1613


Dictionary Entries Near Rubicon

Cite this Entry

“Rubicon.” Dictionary, Merriam-Webster, Accessed 19 May. 2024.

Geographical Definition


geographical name

Ru·​bi·​con ˈrü-bi-ˌkän How to pronounce Rubicon (audio)
river 15 miles (24 kilometers) long in north central Italy flowing east into the Adriatic Sea

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