Roman Army before and after the Marius' Reforms

[Bryan]

There really isn't enough detailed information about Late Republican or later battles to really answer how deep they customary fought.

At Pharsalus, Pompey's first line was 10 deep, to match the length of his line, Caesar's understrength cohorts would have been at no more than 4 ranks deep.

More info about other secondary sources here.
http://www.romanarmytalk.com/thread-24957.html