The most significant test to cohesion that any military unit can experience is combat. It is an environment where the social and vertical bonds that tie soldiers together are subject to intense physical and psychological stresses. The ancients recognised the value of social bonds in combat. It was sometimes stated that men facing death in combat ‘will gladly die in good company’, or that men fought best where ‘brother stands in rank beside brother, friend beside friend, lover beside lover’. This chapter begins by outlining the predisposing factors that might affect a unit prior to the engagement and reflects on how they work to make rout, flight and the loss of cohesion on the battlefield more likely. The psychological and physical pressures leading up to battle, then, could often have an important role in undermining cohesion during combat.