legion marching formations

[tonyodysseus]

I'm sure this is very old hat for many of you, and perhaps there is an old thread someone could direct me to, but I am very curious about Roman legion marching formations. Did they have different ways of doing this? I am now reading Caesar de Bello Gallico, 1.49 and he says that he led his troops "acieque triplici instructa" which means something like laid out in a triple line. Could someone please tell me what would that have looked like? Thanks. Tony