Das fuchst mich jetzt. Ich hab' einmal Gemini befragt; hier die Antwort:
Here are some role-playing game (RPG) books and systems set in the Roman antiquity:
Lex Arcana: This is a classic example. It's a fantasy RPG set in a supernatural and myth-infused version of the Roman Empire, where the players are members of the "Custodes," an elite corps of agents serving the Emperor.
Age of Antiquity: A campaign setting for the 5th Edition of the world's most popular RPG, this book provides a guide to the ancient world, including Rome, Babylon, and Egypt. It includes new cultures, pantheons, subclasses, spells, and magic items.
Mythic Rome (for Mythras): A supplement for the Mythras system, this book is specifically designed for historical, non-fantasy Roman play. It is particularly focused on the Roman Republic.
Weird Wars: Rome (for Savage Worlds): This is a setting that combines the historical backdrop of the Roman Empire with elements of horror and the supernatural. Players fight both historical enemies and monstrous creatures.
Cthulhu Invictus: This is a supplement for the Call of Cthulhu RPG, which transports the Lovecraftian horror setting to ancient Rome. Players take on the role of investigators fighting against the Mythos in the Roman Empire.
GURPS Imperial Rome: A sourcebook for the GURPS system, this book provides a detailed look at the culture and setting of the Roman Empire, allowing for a wide range of campaigns.
Requiem for Rome: This is a supplement for the Vampire: The Requiem system, which focuses on the political intrigue and machinations of vampires in the Roman Republic and Empire.