my favorite pre-marian formation is adapted (aka stolen) from scipio africanus's battle formation against a straight assault

p=pricipes
h=hastati
v=velites
t=triarii
c=cavalry

tttttttttt hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh ttttttttttt
tttttttttt hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh ttttttttttt
pppppp vvvvv pppppp vvvvvv pppppp vvvvvv
pppppp vvvvv pppppp vvvvvv pppppp vvvvvv
pppppp vvvvv pppppp vvvvvv pppppp vvvvvv


c c
cc cc
ccc ccc
cccc cccc


velies hit enemies from behind hastati. when hastati's formation crumples (it will...sissy bastads ) then the enemy imediatly engage principes , velites still pounding them, and then (if all goes well) the triarii turn in to flank the enemy
cavalry mainly there to stop flanking of any formation also good to get around the enemies backs
this is best aganst enemies who outnumber you especially greek and carthaginians what do you think