The use of cavalry was pretty much limited to scouting and used in the slaughter of fleeing enemies. The cavalry was alomst exclusively made up of paid mercenaries, most often from enemy tribes of the tribes the Romans were fighting. The US cavalry used Indians in the same way. Guess where they got the idea? These tribes were promised in some cases citizenship or dominion over the new lands. Often they fought to relieve the pressure of these tribes as they were forced onto thier lands by eastern tribes from the steppes of asia and Russia. The Germans were just beginning to feel these pressures and the reason for moving west. Large cavalry formations were very ineffective due to the heavy forresting. It was said that a man could travel from Gaul (France) to the plains of Poland (the gateway to europe from the east even today)without seeing the sky due to the thick canopy. While greek fire was a later invention, the use of burning oil was extensively known and used. The recent discovery of a Roman cavalry saddle has been reproduced, and it has been found that the thighs were securely wedged allowing very good support and stability, although they could not lean into a lance as the Normans did to subdue the Saxons. They could use their longer swords, shorter shields, and could throw spears very effectively. The gladius was a thrusting, slashing sword. The celtic and german swords were long, hacking blades to take advantage of the superior size and strength of their users. The pilums were thrown to unshield the enemy as described above to allow the roman infantry to press forward in formation. The roman shields were curved and 2/3 body length. They were used in many ways as seen in the movie, but the shorter romans would get up under the larger germans and using their leverage with the shield, would thrust upward under the ribcage or loins of their opponents in short quick slashing thrusts, usually severing vital organs or arteries. The germans needing more room to swing their weapons were unable to use their weapons to best effect. When the legions were defeated by the Germans earlier under Augustus (led by a previous ally), it was because they were caught in the forrest unable to take advantage of their superior organizational skills, and cut up in individual small unit battles that lasted for days. Augustus was heard to cry out the end of his days for the roman commander to "give me back my legions."