In the fourth book of the Histories, Polybius criticizes the failed Aetolian attack on Aegeira. The attackers were reckless, he argues, because they acted as if 'the occupation of a foreign city is finished when one is once within the gates'; in other words, they dispersed too quickly to plunder and did not take adequate measures to subdue the population (Polyb. 4.57.11; trans. Paton). Consequently, the Aegeirans rallied, counterattacked, and defeated the scattered Aetolians. Polybius brings up an important point: in ancient Mediterranean warfare, the final capture of a city was not assured simply because the walls were breached. After breaking through the outer defenses, attackers faced unfamiliar streets and the threat of counterattack. Moreover, local resistance could (and did) become atomized into street-by-street, building-by-building combat. In order to understand how ancient armies coped with these dangers, and how they operated once within enemy cities, this paper examines the critical moments after the breach. Utilizing evidence from Greek and Roman sources, as well as comparative evidence from other historical periods, it argues that attacking forces generally made a concerted effort to seek out and eliminate any remaining challenges within the targeted town. To this end, they maintained 'cohesion' – i.e., 'collective combat performance' or the ability 'to act together and to achieve their mission in the face of the enemy.' Specifically, attackers stayed together in small units, detachments, or ad hoc groups as they made their way through enemy streets, assaulted last bastions like forts and citadels, and suppressed the final pockets of enemy resistance. Additionally, although communication was difficult in urban environments, commanders and officers might coordinate their subordinates in these final efforts to subdue the defending population.