Ok heres my pre-marius formation in SPQR, (i only use it against gaul or other barbs)
"THE RUBBER BRICK"
T__T_P_P_P_P_P_T__T
H__H_H_H_H__H
C V_______V C
G
Key:
T=Triarii
P=Principes
H=Hastati
V=Velites
C=Cavalry
G=General
My principes in shield wall, whith hastati support, pins the enemy down while velites pepper them and lowers their morale, and triarii guards the flanks. And my cavalry fights of possible enemy cavalries flanking maneuvers, and when that is done i bring my cavalry around the flánks and attacks the enemy in his back. And now while surrounded, gauls break almost at once.