When Raziel returned from the Abyss after his execution, emerging in Kain's empire, his first thoughts were regarding the safety of his clan, thus he travelled to his clan territory. He ultimately discovered the Stronghold empty and long abandoned.
Raziel took this as evidence of a genocide against his clan by Kain further motivating his hatred against his former master.
Nosgoth suggested that Raziel had ordered his clan to abandon their original underground city and the Fane beneath the Erebus Mountains to move here in the early years of Kain's empire. After Raziel's execution and Kain's disappearance the other clans, believing they were doing Kain's will, had turned on the Razielim and invaded their territory - dividing the spoils of their conquest ultimately led to conflict and the beginning of the Vampire civil war.
Some time later a group of fledgling Razielim led by Eskandor, who had been covertly stored in the abandoned Fane, returned to the Razielim territory to find it occupied by the Dumahim. Revealing the human victories at Coorhagen seen from the skies on his journey, Eskandor and his brood were spared and the clans called a truce to put down the human resistance and begin the War for Nosgoth.
Raziel's clan territory is never named in Soul Reaver and there are currently no clues as to its name.
The Razielim may have indeed been wiped out by Kain, but Raziel's clan territory provides little evidence of this. The only evidence are blood stained shields mounted on walls, but apart from this, it is totally empty and there are no signs of a struggle or bodies (unlike what is shown in Dumah's territory, The Ash Village ), though this may be because the genocide of Raziel's clan happened centuries before that of Dumah's clan.