Have you read Tom Holland's Rubicon? No? You should. It's very good. Perhaps not as good as Persian Fire, which impressively pulls together all sorts of stuff about Greek warfare and Persian imperialism into a spectacular read, but very good for all that.
I've never seen the Rubicon, oddly enough, though I'm told that it's a piddling little affair, less impressive even than Cannae's underwhelming Aufidus. The rivers of the Classical world, so magnificent in our minds, tend to be disappointing affairs. Heinrich has described Sparta's Eurotas as one of the greatest rivers in Greece, by which he meant, he added, that it's not unlike the Liffey at low tide.
So it seems that despite, say, the startling decrepitude that they foisted on Cato the Younger, the makers of Rome had at least that much right, with Caesar gently sploshing across a muddy stream, rather than charging full-tilt into a mighty river, which is the natural way to picture it.
What do mean you have no idea what I'm talking about? Look, the Rubicon, pathetic though it may have been, was the traditional boundary between Italy proper and what the Romans called 'Cisalpine Gaul' - Rome this side of the Alps. Caesar's military writ ran only outside of Italy in the provinces allocated to him, and by crossing the Rubicon in force in 49 BC he plunged Rome into Civil War, presumably feeling that the Romans had had a generation to recover from the mess that was the whole collapse of the Republic between 91 and 71 BC, allowing from that enervating squabble that was the Catilinarian Conspiracy.
Appian describes it best, I've always thought:
When his course brought him to the river Rubicon, which forms the boundary line of Italy, he stopped and, while gazing at the stream, revolved in his mind the evils that would result, should he cross the river in arms. Recovering himself, he said to those who were present, "My friends, to leave this stream uncrossed will breed manifold distress for me; to cross it, for all mankind." Thereupon, he crossed with a rush like one inspired, uttering the familiar phrase, "The die is cast: so let it be!" - Civil Wars, 2.35
If I was really efficient, I'd have told you about this last Wednesday, but, well, I'm not. Anyway, today's good enough.