Quote Originally Posted by CaesarAugustus
I though that the Rubicon would have marked the border into Italy. So why was it such a big deal for Caesar to have crossed that one little river one third of the way down Italy?
The Rubicon was the border between the territory of Rome and the province.

I think Caesar was proconsul of the provinces of Illyricum, Gallia Togata (Cisalpine Gaul) and Gallia Transalpina, plus of course the new provinces that he erected. Proconsul means "for the consul", so he had the full power of the consules for this determined territory. In Italia reigned the real consules of course, so it was a really severe crime to bring a legion into Italia. It was a bit like starting a world war.