I bought this supplement because I was beginning my campaign in Arcanis, which has a Roman analogue. Eternal Rome is quite accommodating of alternate histories, featuring a "What If?" section in the first chapter. It covers the various regions contemporary with Rome and their opinions of Romans (hint: not very good).
The second chapter digs into the guts of D20 systems and modifies them appropriately: steppe barbarians don't rage, bards are divided into Celtic and Orphic types, druids are more like their historical counterparts (a change near and dear to my heart, as I've been railing against the "hippy druid" portrayal for over a decade), and the new gladiator class is reminiscent of the same class from the Advanced Dungeons & Dragons 2nd Edition Complete Gladiator's Handbook. Like the 2nd-edition version, the 3rd-edition version is powerful. This is a fighter class with the uncanny dodge chain and a host of other abilities including bonuses to combat, from weapon styles and preferred opponents. Strangely, this section downplays paladins ("The Romans didn't regard spellcasting as compatible with the virtues of the warrior...") but gives the vigil prestige class access to spells. There are surprisingly few classes focusing on the legendary Roman fighting styles and, to my disappointment, no professional legionnaire core class.
Feats and skills round out the third chapter, many of them superseded by Complete Warrior.
Chapter four is where Eternal Rome distinguishes itself from other supplements with its Fame score. This is the much vaunted distinction between a Roman-style game and a typical fantasy sword-and-sandals epic: politics. Be it senators or gladiators it details a range of bonuses and penalties that come about from being famous or infamous. The equipment chapter is fifth and features the full range of gladiatorial weapons and armor.
Roman magic covers the sixth chapter, which features the usual spells and magic items. It's distinguished by two entries, the evil eye and the Legion Eagle. The Eagle Standard figured prominently in my campaign and the description does it justice, but treats it as an artifact without explaining how these important staples of Roman warfare were created. Making them artifacts changes the role of the wielder (an aquilifer, which was the role of my character in the Arcanis campaign) significantly.
The monsters chapter features such well-trammeled territory as the catoblepas, fury, hippocampus, and siren. There are also two races, nymph and satyr - anyone remember the half-nymph and half-satyr article from Dragon Magazine?
Chapter eight fleshes out the Roman world and places for adventure. Chapter nine is a historical primer, although game masters would be better-suited picking a period in Roman history and doing their own research. The ninth chapter covers Roman culture and is by far the most valuable for a game master planning a Roman campaign. Chapter eleven details Roman religion which is better represented in other works but still relevant here for its cleric rules. The book concludes with an adventure for 4 to 6 1st-level characters in which they visit a Sibyl. I would have preferred fleshed-out NPCs, like the patron Strabo who makes a cameo in the adventure along with a map of his estate.
Eternal Rome takes on a massive topic and does its level best to encompass all of Roman history, myth, and legend in one book. Although it struggles in parts to cover every aspect of Roman life, Eternal Rome lays a solid foundation to launch a campaign. It will still require a considerable amount of effort on the game master's part, and probably a few other gaming supplements, to fully flesh-out a Roman campaign.