Rome engaged in military and diplomatic expansionistic state behavior, which we now describe as 'imperialism, ' since well before the appearance of ancient sources describing this activity. Over the course of at least 800 years, the Romans established and maintained a Mediterranean-wide empire from Spain to Syria (and sometimes farther east) and from the North Sea to North Africa. How and why they did this is a perennial source of scholarly controversy. Earlier debates over whether Rome was an aggressive or defensive imperial state have progressed to theoretically-informed discussions of the extent to which system-level or discursive pressures shaped the Roman Empire. Roman imperialism studies now encompass such ancillary subfields as Roman frontier studies and Romanization.