I have compiled some facts about Geroian history in from older versions of Mount&Blade till Warband:
-Geroia is a place within Calradia(thow is not shown on map) that is ruled by a Count named Arriases.
-Geroia lies situated on the border between Nords and Swadians(warband)/Rhodoks(vanilla)(Zendar was fully in nord territory) according to the older versions.
-Geroia is a neutral faction.
-Geroia's most powerful city was Zendar,independent and neutral,but was destroyed by Sea Raiders that settled in the north.
-Geroia was a rich faction and the Salt Mines near Zendar made that Geroia supported all Calradia with Salt.
-Count Arriases of Geroia still lives,and his stronghold is Castle Geroia,according to Rolf's story.
-"Geroia" and "Arriases" names as well as the "Count" title suggest that Geroia is based on medieval France.