The Triplex Acies is the usual battle formation in the Roman Army.  This setup included three parts.  The Acies Prima, was the strongest and forerunning line of defense.  This first line consisted of four cohorts.  The Acies Secunda online had three cohorts.  Their purpose in battle was to fill in the holes of the first line whenever men formed gaps.  This line often contained mediocre soldiers.  The last was the Acies Tertia.  This weak set of three cohorts was used to protect against flanking and in case the second line needed extra men to help fill in the first line.

Then there were the signals used in battle.  The first signalling device was called the Cornu.  This horn had a deep loud sound that was blown for basic formations.  The Tuba, which looked like the trumpet we have today, gave precise battle commands.  The Bucina was a lot like a bugle.  The Bucina told the soldiers when lunch breaks were happening and signaled preliminary formations.  Last but not least, the Lituus was used to signal the cavalry.