Discipline in the Roman Army was very strict, without it the Roman Empire could never have been made. If a soldier disobeyed orders, he was beaten, if a whole legion rebelled, one in ten men were killed.
The Primus Pilus is one of the lower-ranking officers in the Roman Army, he is the senior centurion, the one who leads charges and gies orders directly on the field. The highest ranking officer is the Legate.
He is incharge of a whle legion, and wears a fancy helmet with wings on the sides. He is assisted in command by six Tribunes, who give advice and the like.