The series includes games using the same core system, with however lot of specific rules for each of them. One player defends the interests of Roman empire (the "legal" one), while the other defends those of their enemies (barbarians and usurpers). The players' roles may be swapped during the game.
Alea Iacta Est (49-29 BC) - Caesar to Octavianus
Imperator (161-217 AD) - Marcus-Aurelius to Caracalla
Semper Victor (305-363 AD) - Constantin to Julian the Apostate
Ultimus Romanorum (405-490 AD) - Great Invasions of the 5th century, final fall of the Western Empire