On 7 January 49 BCE, the Senate demanded Julius Caesar to hand over his ten well-trained legions to a new governor. Caesar heard the news in Ravenna, and knew that he had to make a choice between prosecution and rebellion; preferring the dignity of war over the humiliation of a process, Caesar chose to rebel, quoting his favorite poet Menander, "the die is cast" (alea iacta est).

On January 10 or 11, his army advanced to Rimini, where Caesar could control the passes across the Apennines: in doing so, he crossed the river Rubico, thereby invading Italy and provoking the Second Civil War. The bridge at modern Savignano probably marks the place where the ancient Via Aemilia crossed the Rubico.
When he came to the river (it is called the Rubico) which forms the frontier between Cisalpine Gaul and the rest of Italy he became full of thought; for now he was drawing nearer and nearer to the dreadful step, and his mind wavered as he considered what a tremendous venture it was upon which he was engaged. He began to go more slowly and then ordered a halt. For a long time he weighed matters up silently in own mind, irresolute between the two alternatives. In these moments his purpose was constantly changing. For some time too he discussed his perplexities with his friends who were there, among whom was [the future historian] Asinius Pollio. He thought of the sufferings which his crossing the river would bring upon mankind and he imagined the fame of the story of it which they would leave to posterity. Finally, in a sort of passion, as though he were casting calculation aside and abandoning himself to whatever lay in store for him, making use too of the expression which is frequently used by those who are on the point of committing themselves to desperate and unpredictable chances, 'Let the die be cast,' he said, and with these words hurried to cross the river. https://www.livius.org/sources/content/plutarch/plutarchs-caesar/plutarch-on-caesars-rubico-crossing/


Marcus Lucanus:
“How swiftly Caesar had surmounted the icy Alps and in his mind conceived immense upheavals, coming war. When he reached the water of the Little Rubicon, clearly to the leader through the murky night appeared a mighty image of his country in distress, grief in her face, her white hair streaming from her tower-crowned head, with tresses torn and shoulders bare she stood before him, and sighing said:
‘Where further do you march? Where do you take my standards, warriors? If lawfully you come, if as citizens, this far only is allowed.’
Then trembling struck the leader’s limbs; his hair grew stiff and weakness checked his progress, holding his feet at the river’s edge. At last he speaks:
‘O Thunderer, surveying great Rome’s walls from the Tarpeian Rock —
‘O Phrygian house gods of Iulus, clan and mysteries of Quirinus who was carried off to heaven —
‘O Jupiter of Latium, seated in lofty Alba and hearths of Vesta —
‘O Rome, equal to the highest deity, favor my plans.
Not with impious weapons do I pursue you. Here am I, Caesar, conqueror of land and sea, your own soldier, everywhere, now, too, if I am permitted. The man who makes me your enemy — it is he who be the guilty one.’
Then he broke the barriers of war and through the swollen river swiftly took his standards. And Caesar crossed the flood and reached the opposite bank. From Hesperia’s forbidden fields he took his stand and said:
‘Here I abandon peace and desecrated law.
Fortune, it is you I follow.
Farewell to treaties.
From now on war is our judge.'”
Hail, Caesar: We who are about to die salute you.