In Greek and Latin historical narratives, Roman armies are repeatedly said to destroy enemy communities, both their physical urban spaces and inhabitant populations. Some ancient authors claim that this conduct was characteristic of the Roman way of war, particularly during the period of the Middle Republic. However, this seemingly prevalent feature of Roman warfare remains poorly understood. Ancient descriptions of urban destruction and mass killing are often vague or formulaic, and rarely indicate how or why this violence took place. Although a few modern studies have examined mass violence in antiquity, the destruction of communities is seldom treated as a distinct category of Roman military action, with its own methods and motives. Furthermore, there has been little effort to explore how ancient armies actually destroyed cities or peoples using pre-modern tools. To redress these gaps in the scholarship, this dissertation aims to demonstrate how and why Roman armies destroyed urban spaces and populations. The project first examines descriptions of urban destruction and mass killing in ancient texts, archaeological and art historical evidence of mass violence, and comparative evidence from other historical periods. The second half of the project investigates individual cases in which Roman commanders attacked and destroyed enemy cities or populations. Case studies allow in-depth examinations of individual events, making it possible to situate episodes of mass violence within a larger set of historical circumstances; this approach highlights the specific causal factors that encouraged Roman military leaders to target enemy communities. Using these methods, this dissertation argues that ancient armies employed demolition and mass arson to destroy urban spaces, and killed populations using cold-blooded mass executions or hot-blooded indiscriminate massacres. Although ancient military forces rarely, if ever, razed entire towns or exterminated whole peoples, even partial destruction required an expenditure of time, labor, and resources. Thus the destruction of communities was not the result of haphazard outburst or violent frenzy, but stemmed from the calculated decisions of military and political leaders. This study further argues that Roman commanders destroyed enemy communities instrumentally, to accomplish a range of goals and objectives. While many Roman commanders employed mass violence strategically, as a response to specific military problems, their political, economic, and personal goals could also motivate destruction and mass killing in war.