Sulla was a general on account of Marius, they guy that reformed the armies. When the Samnites, or more correctly, the Italians, rebelled against Rome in 91 BC, Sulla commanded 13 legions! That's about 62,400 men, not to mention auxilliaries and support trains.

So, I figured that if you have a stack of 20 Hastati at large unit size (this is 80 men per unit which is historically correct if you consider 1 RTW unit equal to 1 Roman century) you have only 1/3 of a legion!

Multiply that by 39 to compare it with Sulla's army.

Note: This 13 legion force was only to expel a few rebels, imgaine waging war with Carthage!