The role of centurions in Roman warfare has never been decisively established. Historical sources suggest that centurions exerted an influence on the performance of the Roman battle line that was highly disproportionate to their numbers, as well as to their particular actions. However, the lack of a formal framework of Roman tactics does not allow this proposition to be tested. The results obtained from an agent-based model (abm) of Roman warfare, a computer-simulation technique, however, suggest that battle formations benefited greatly from the presence of even a small percentage of psychologically resilient soldiers, especially along the first line, even if these individuals displayed no more than average levels of skill and aggression. Hence, the model’s simulated patterns of Roman warfare indicate that the multiple roles performed by the centurions as described in the sources were not distinguished so much by tactics as by experience and imperviousness to the stress of combat.