On the checkerboard formation

[The Internet]

With the enemy they faced (barbarians mainly) they faced an enemy that charged in groups (tribal groups mainly) so the Romans never had to deal with their entire front line being over-run. To deal with these tribal groups they had their own "groups" to combat them (their groups obviously being the maniples of hastati and principes) and then they added their own twist on it by giving the army a system where they were able to rotate and refresh the front ranks to keep the frontline fresh, unlike the barbarians who got tired out and over-powered.


Thats my take on their military layout anyway, it can never really be confirmed or denied unfortunately.