Kehjan was the capital city of a land by the same name during the Sin War located somewhere on the eastern continent. The town was the center of commerce and political power during the time, housing the mage clans of the time as well as lying very near the two main temples of both the Cathedral of Light and Triune.
It is unknown where exactly Kehjan was located, but it is known that Toraja was only a few days away, and seeing as the map of present day Sanctuary names the jungles in the southern parts of the world precisely this, Kehjan was perhaps located there.
Kehjan was without a doubt the largest city in the region at the time, but it's unclear whether it is the largest in the world. Few references are made to any georaphical locations outside of Kehjan, but there appear to be other cities around the world accessible by ship. Still, the Three chose the region around Kehjan to the the site of their own cult, so perhaps it was the most heavily populated.
|Locations in the Diablo Universe|
|Planes||Black Abyss • Burning Hells • High Heavens • Sanctuary • Trag'Oul's Realm • The Void|
|Regions in Sanctuary||Aranoch • Dreadlands • Entsteig • Kehjistan • Khanduras • Mount Arreat • Scosglen • Skovos Isles • Torajan Jungles • Westmarch • Xiansai|
|Towns in Sanctuary||Bastion's Keep • Bramwell • Caldeum • Duncraig • Gea Kul • Harrogath • Hashir • Istani • Ivgorod • Kalinash • Kehjan • Kingsport • Kurast • Lut Gholein • New Tristram (Old Tristram) • Partha • Rogue Encampment • Seram • Staalbreak • Toraja • Tran Athulua • Tulisam • Tur Dulra • Ureh • Urjhani • Viz-jun • Westmarch|
|Other Places||Pandemonium Fortress • Silver City|