Concentrating on the late medieval period, Age of Chivalry: Hegemony replaces or significantly alters each of the civilizations in the original game, while adding a number of new ones, allowing the player to control Central and Western European states. Many new units and technologies have been added and gameplay dynamics have been changed considerably in this complete overhaul of Age of Empires II.
Just a little update to show this is still being worked on. I will soon release a beta version of the new expansion, which will introduce the Papal States, Naples and Hungary to Age of Chivalry. Not all graphics will be complete yet - the version will mostly serve as a way of discovering bugs with the new civs and making sure everything works smoothly.
Until then, enjoy this screenshot, which shows off some Italian buildings in medieval Florence. I've added the famous Campanile (the bell tower next to the cathedral) made by Giotto. It can't be built in random maps, but you can use it in your scenarios. The screenshot also shows the Neapolitan Princely Court - the large square building with inner courtyard.