Ab Urbe Condita is an overhaul for Rome: Total War, featuring an array of additional content, including new units, an AI scripting system, an AOR mercenary system, an expanded campaign map and graphical improvements (among many other amendments).
This version is a massive improvement on earlier versions, including a new faction and new units.
AUC (v2) changes are as follows:
* It now runs on Alexander.exe; this was necessary in order to incorporate the new additions. Furthermore, the AI performs much better now (including naval invasions).
* A small AOR system has been included: nothing fancy, just a few mercenary units that are now recruitable in various regions dotted throughout the map.
* A new fully fleshed out faction: The Arabian Kingdom of Sabaea
* Many new units (about 50-60 in all I think)
* The popular "Force Diplomacy" script has been added; now in diplomatic discussions, press the ? mark at the top of the screen to force the enemy faction to accept your terms (try not to abuse it; it is intended to counter the daft AI)
* Many new re-skins of pre-existing units.
* New AI Advisors
* New Battlemaps
* And many more wee additions!