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 is the near final version of AUC; changes include bugfixes and reskins.
AUC (v4) changes are as follows:
* Most remaining bugs and crashes fixed.
* Filling in the "blanks"; i.e. added proper UI cards for rebel units, text inconsistencies fixed, new rebel generals etc.
* Some reskins and new units (notably the Macedonian Royal Guard and Praetorian Guard).
* Few cultural oddities fixed (notably the Zoroastrian temples in Arabia).
* New mines in Arabia and North Africa (to boost the flagging economies there, particularly for Sabaea).