How many soldiers/legions did Caesar cross the rubicon with?

Question

How many soldiers/legions did Caesar cross the rubicon with?

Answer 1

On January 10, 49 BC Caesar crossed the Rubicon with one legion, the Legio XIII Gemina. They were veterans. The size of a typical legion varied widely throughout the history of ancient Rome, with complements of 4,200 legionaries and 300 equites in the republican period of Rome, (the infantry were split into 35 maniples of 120 legionaries each), to 5,200 men plus auxiliaries in the imperial period (split into 10 cohorts, 9 of 480 men each, plus the first cohort holding 800 men).

Answer 2

Not all that many. Armies tended to be much smaller then than now.  He probably had two or three legions under his command in Gaul, but did not bring all of them to Rome.  I would guess 12,000.