Crossing the Rubicon: Meaning, What Happened in 49 BC, and What Caesar Said

Start hereCaesar wrote his own account of the civil war that began in 49 BC. It does not mention the Rubicon. So where does the famous scene at the river come from?

To cross the Rubicon means to take a step you cannot take back. The phrase comes from Julius Caesar. The Rubicon was a short river of north-central Italy, and Caesar’s crossing of it with his army in 49 BC began a civil war. This page starts with the saying, then follows what the ancient writers say happened at the river.

011. What the phrase means

Cambridge Dictionary defines cross the Rubicon as “to do something that you cannot later change and will strongly influence future events”. The American Heritage Dictionary calls a Rubicon “a limit that when passed or exceeded permits of no return”.

The American Heritage Idioms Dictionary says the figurative English use had appeared by the early 1600s. Its example is someone handing in a resignation.

022. Why a small river mattered

The Rubicon was a small river and a border. Lewis and Short’s Latin dictionary calls it “a small river on the east coast of Italy, which formed the boundary between Italy and Cisalpine Gaul”.

Plutarch says the Gaul along the Po was part of the province assigned to Caesar, and that the Rubicon separates it from the rest of Italy. Suetonius calls the river “the boundary of his province”, and Appian calls it the boundary of Italy.

Crossing it with soldiers was the problem. Pietro Romanelli wrote the Rubicon entry in the 1936 Enciclopedia Italiana. He says no magistrate could cross the river at the head of an army without the senate’s authorisation.

He adds that it is not quite certain when the boundary was moved to this river, though it seems certain that Sulla fixed it there.

Cicero shows the general rule at work in another case. He was attacking a governor who had led his army out of Syria into Egypt.

A governor, he says, may not leave his province, lead out an army or wage war on his own initiative. Nor may he enter a kingdom without the order of the Roman people or the senate. Many old laws forbid this, he says, and above all the Cornelian law on treason and the Julian law on extortion.

None of the accounts of the crossing that we read names the law Caesar broke. Our reading: the rule is clear in outline, but these sources do not say which law he would have been tried under.

033. When it happened

Caesar’s own account dates the senate’s emergency decree a.d. VII Id. Ian., the seventh day before the Ides of January. By the Roman way of counting, that is 7 January. The Loeb translator of Plutarch gives the same date, January 7, 49 BC, for the day Antony and Curio were driven from the senate.

The decree told the consuls, praetors, tribunes and proconsuls near Rome to see that the state came to no harm. The tribunes fled the city at once and went to Caesar, who was then at Ravenna.

The crossing followed, in January 49 BC. None of the ancient accounts we read gives its day.

That January did not line up with the seasons. Before Caesar’s reform of the calendar in 46 BC, the Roman year had 355 days, which was too short for the solar year.

Suetonius says it had drifted so far that the harvest festivals no longer came in summer. The Loeb translator of Plutarch notes that by 46 BC it ran more than two months ahead of the solar year.

So any date on our calendar is a conversion. Romanelli’s 1936 entry dates the crossing to 23 November 50 BC, without saying how he reached it. Our reading: it looks like the Roman January turned into a solar date, which would put the crossing in late autumn.

Lucan’s poem, by contrast, has a winter river, swollen by rain and by melting Alpine snow.

044. What the ancient writers say happened

Doesn't hold up Caesar’s own account names the Rubicon. Caesar’s own Civil War does not mention the river: book 1 simply says he “set out for Ariminum with that legion”. That legion was the Thirteenth. The famous scene comes from later writers.

Suetonius

In Suetonius, Caesar hid his plans: he watched a public show, looked over plans for a gladiator school and joined a banquet. After sunset he left with a small company, in a carriage pulled by mules from a nearby bakeshop. His lights went out, he lost his way, and he found a guide only at dawn.

At the river he paused and said: “Even yet we may draw back; but once cross yon little bridge, and the whole issue is with the sword”.

Then, Suetonius says, a sign appeared: a being of wondrous stature and beauty, playing on a reed pipe. It snatched a trumpet from one of the trumpeters, sounded the war-note and strode to the far bank. Then Caesar spoke the line about the die.

Plutarch

Plutarch has Caesar watch gladiators, dine with guests and slip away at dusk in a hired cart, at first by another road. At the river he “communed with himself a long time in silence as his resolution wavered back and forth”. He talked it over with the friends who were with him, among them Asinius Pollio.

At last, as if giving up calculation, he hurried across and took Ariminum before daybreak. Plutarch puts his force at no more than three hundred horsemen and five thousand legionaries.

Appian

In Appian, Caesar leaves a banquet pleading illness and drives toward Ariminum, his cavalry close behind. At the river he stops, gazes at the stream and thinks over the evils that crossing in arms would bring. Then he says: “My friends, to leave this stream uncrossed will breed manifold distress for me; to cross it, for all mankind”.

Lucan, a poem

Lucan wrote his epic about the civil war under the emperor Nero, and died in AD 65. It is poetry, not a report. In it, Caesar sees “his trembling country’s image” on the bank, telling the soldiers to go no further.

Who wrote these, and when

• Suetonius seems to have written mostly under the emperors Trajan and Hadrian (AD 98–138), and was for a time Hadrian’s secretary.
• Plutarch lived about AD 45 to 120 and is thought to have written his Lives in his later years.
• Appian, a historian from Alexandria, writes of events “in my time” under the emperor Trajan.

So all three wrote more than a century after the crossing. They did have older material. Asinius Pollio, whom Plutarch places at the river, later wrote a history of the civil wars. The 1911 Britannica says Plutarch and Appian used it as an authority. Almost all of his writing is lost. Suetonius reports that Pollio thought Caesar’s own memoirs were put together “without strict regard for truth”.

Our reading: the details differ, but in every later account we read, Caesar stops at the river before he crosses.

055. What Caesar is reported to have said

Partly At the river Caesar said “alea iacta est”. The sources disagree on the words and on the language. There are two wordings, one Latin and one Greek.

Source	Language given	The words as given
Suetonius, Julius 32	Latin; he does not say what language Caesar spoke	Iacta alea est, The die is cast
Plutarch, Caesar 32 and Pompey 60	Greek, and Pompey 60 says Caesar spoke Greek	ἀνερρίφθω κύβος, Let the die be cast
Appian, Civil Wars 2.35	Greek, the same saying as Plutarch’s; he does not say what language Caesar spoke	ὁ κύβος ἀνερρίφθω, The die is cast: so let it be! (White’s translation)

Suetonius’s word order is iacta alea est; the familiar alea iacta est reverses it. Plutarch’s life of Pompey says Caesar was “calling out in Greek to the bystanders these words only, ‘Let the die be cast,’” as he took his army across.

In his life of Caesar, Plutarch calls it “the phrase with which men usually prelude their plunge into desperate and daring fortunes”. Appian, too, calls it a familiar phrase. His Greek is the same saying as Plutarch’s; the English versions differ only because the translators differ.

The Greek line also appears elsewhere. The same Greek saying turns up in a comedy by Menander, quoted by Athenaeus, where it is about getting married. The line reads δεδογμένον τὸ πρᾶγμ· ἀνερρίφθω κύβος, “the thing’s decided; let the die be cast”. Plutarch does not name Menander. Our reading: in Plutarch’s and Appian’s telling, Caesar reached for a well-known saying.

In Latin, alea is a game with dice, and more generally a game of chance. Our reading: a die that has been thrown is still rolling. The choice is made, but the outcome is not yet known.

A separate page on alea iacta est goes further into the words. We also set it beside other famous sayings in Latin Phrases, Checked.

066. Which river is the Rubicon today?

Still argued The modern Rubicone is Caesar’s Rubicon. Romanelli wrote in 1936 that it cannot be said with certainty which small river it was, because the ancient itineraries and writers do not clearly agree. He adds that perhaps it is also hard because the streams’ courses partly differ from what they must have been in antiquity. He named three candidates, disputed even among modern scholars: the Pisciatello, the Fiumicino near Savignano, and the Uso near Santarcangelo.

• The lower course of the Pisciatello is called the Rigone, which he says seems to be a corruption of the ancient name.
• Lewis and Short’s 1879 Latin dictionary had called the Rubicon probably the modern Pisatello.
• The name Rubicone has been given officially to the Fiumicino.

The town beside the Fiumicino was called Savignano di Romagna until 1933; it became Savignano sul Rubicone. A 2010 review in the University of Bologna journal AlmaTourism counted the Rubicon among the “long-standing issues” that a book on Caesar and Rimini did not try to resolve. Our reading: an official name settles the label on the map, not the question of history.

077. What came next

Plutarch writes that after Ariminum fell it was as if war had thrown open its gates, and the laws of the state were confounded along with the boundaries of the province. Pompey fled to Brundisium and sailed away before Caesar could stop him. Plutarch says Caesar became master of all Italy “in sixty days and without bloodshed”.

The war went on for years. Caesar defeated Pompey at Pharsalus in 48 BC, and Pompey’s sons were crushed at Munda on 17 March 45 BC. On 15 March 44 BC Caesar was murdered in the senate house. His whole life is in our summary of Julius Caesar.

The river did not stay a border. Pliny the Elder’s Natural History lists the Rubicon as “once the boundary of Italy”.

088. How to use the idea

These are our readings of the story, not rules from it.

• Pause before the bridge. In every later account we read, Caesar stops before he crosses. Doubt can be part of a big decision, not a failure of nerve.
• Name the step that cannot be undone. Ask which single act makes a choice permanent, such as a signature or a public statement.
• Check whether it really is a Rubicon. Many choices feel final and can still be reversed. Save your caution for the ones that cannot.
• Read the oldest account you can find. Caesar’s own book does not mention the river. The famous scene comes from writers born long after.

Mental Models from History looks at crossing the Rubicon beside other sayings used as thinking tools.

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How we checked this · Last checked October 2026

• We read Suetonius, Plutarch and Appian in the Loeb translations on LacusCurtius, Caesar's Civil War, Cicero and Pliny in Latin, and Lucan in Sir Edward Ridley's 1896 translation.
• We searched all three books of Caesar's Civil War for the river's name. It does not appear.
• The date 7 January is worked out from Caesar's Latin with the counting rule in Allen and Greenough's Latin grammar, and it matches the Loeb translator's note. One English translation of the Civil War gives a different day, so we did not use it.
• None of the accounts of the crossing that we read gives its day or names the law Caesar broke.
• We read Appian's Greek on Perseids. His words for the line about the die are the same as Plutarch's.
• We could not confirm the year the Fiumicino was officially named Rubicone. We give only the town's renaming, from the 1936 Enciclopedia Italiana. The newest source we read on which river it was is a 2010 review in AlmaTourism.

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