"The Roman legion was supposed to operate with wide gaps between its maniples and significant intervals between each of the three lines. The openness of its formation allowed the legion to advance without falling into disorder even over comparatively rough terrain. It is impossible, even for well drilled troops, to march in a perfectly straight line, and the more uneven the terrain, the more probable that a unit will veer to one side or the other. The wide intervals between the maniples of the legion allowed them to cope with such deviation without units colliding and merging together and ceasing to be independent tactical entities. The unusual formation adopted by the Roman infantry at Cannae sacrificed this openness and with it most of the flexibility of the manipular system."