Quote Originally Posted by Celt Centurion
I did have the good fortune once though of being one of the Roman Factions with one army of about 1,600 men with fully upgraded armour. SPQR attacked me with two armies, also of about 1,600 men each, but they had not taken the time and expense of upgrading their armour. I nearly had the battle won when SPQR's reinforcements showed up from the City. I let my cavalry chase down the ones running away, and sent the rest of my army as high on the hill as the red line would allow. My Legionary Cohorts still had about 30% of of their missiles. When the cavalry was done, I let them rest. By the time that the SPQR army got near my infantry and archers, they were already routing as the uphill has a range advantage over downhill. At the end, I still had over 1,200 men, and SPQR had lost over 3,000.
This happened because the AI units were exhausted. Units get big morale penalties and combat penalties when exhausted, and the AI doesn't realize it. It is possible to turn off fatigue in the preferences.txt file.