Why didn\'t Romans fought in single line?

[Flavivs Aetivs]

Being a bit Rome: Total War specific, here's a test battle I did for IBUR. The quincunx is effectively a static, reactive formation in the game. Very flexible, basically allowing units in the rear to respond to trouble spots quickly and with ease, and the second line of the checkerboard can either let the 1st line be pushed back into it, or pull up to engage. It distorts an enemy line with ease, causing it to break and create key exposures that can be exploited.



Where I re-organized units for relief and other stuff: