The military of ancient Rome had many techniques for fighting; offense and defense which helped them majorly to win most of their battles and wars. Their normal positions were to have the infantry in the middle and the cavalry out on the sides. The main purpose of this method was to prevent the infantry to be out smarted by the enemy flanking them from the sides then if the enemy decides to retreat the cavalry would push forward to hunt them down.
Other techniques:
The wedge was a commonly used technique by the legionaries. They would form up in a triangular shape, the top being one soldier facing towards the enemy which enables them to make 1 on 1 fighting more difficult for the enemy. It would also force the enemies to move into smaller groups which is where the gladius came in handy.
The tortoise was a great defensive method by which the legionaries would hold their shields above their heads except for the front and side rows creating a shell-like armor that would protect them from artillery made by the enemy.
Another good defensive method is the orb. It is kind of similar to the tortoise but the men in the middle don't hold up their shields and it is in a formation of a circle. This tactic is really helpful when parts of the army have been divided during battle.
References:
Websites:
The roman empire 2009, Roman Tactic, viewed 31st March 2010
[http://www.roman-empire.net/army/tactics.html]
Word Press 2010, Ferrel's travel blog, soldier picture, viewed 31st March 2010
[http://ferrelljenkins.files.wordpress.com/2008/04/soldiers_54sm.jpg]
The roman empire, 2009, legionaries picture, viewed 31st March 2010
[http://www.roman-empire.net/diverse/pics/corbridge-legionaries/orb-01.jpg]
Fectio 2008, the wedge formation, viewed 31st March 2010
[http://www.fectio.org.uk/shows/vechten2004drill2.jpg]