# cross the Rubicon

idiom · CEFR C1

Source: https://englishreference.com/idiom/cross-the-rubicon
Updated: 2026-08-10

## Meaning

To take a step you cannot undo.

## Examples

- When she handed in her resignation, she crossed the Rubicon.
- The company crossed the Rubicon the day it shut down the old system, because there was no longer anything to go back to.
- Everyone in the room understood that signing the agreement would cross the Rubicon, committing them to a strategy that could be carried through or abandoned in ruin, but never quietly reversed.

## Origin

The Rubicon was an unremarkable stream in northern Italy, notable only for what it marked: the border between Caesar's province of Cisalpine Gaul and Italy proper. Roman law was blunt about it. A governor commanding an army could not bring that army across the line. To do so was to declare war on the Senate. In January of 49 BC Caesar brought the Thirteenth Legion across anyway, and the Republic never recovered. Suetonius and Plutarch both linger on the pause at the bank — the moment when the thing was still undone — before the order was given. To cross the Rubicon in English is to pass that same kind of line: the commitment after which the old options are gone, whatever happens next.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.