A dreadful city of black basalt, Khisan's imposing jagged towers, sheer walls and gothic arches clutch at the sides of an extinct volcano in the Ruined Land. The top of this mountain city is crowned by the towering fortress of Thaal, the residence of the Lords of Darkness; the council of greater demons that presides over the chaos demons that enter the world through the Dreaming Gate to the city's south.
Khisan is a city of demons, built by demons. Most of the intelligent, anthropoid demons chose to live here, and Khisan's vast armies use the surrounding plains to pratice thier warfare. Occasionally they engage in sorties to the north to attack the people of Tenra or to the northwest to battle with the Lunaris (the dark elves).
Fortunately for the rest of Caevalonia, the Land's Spine mountains make a nigh insurmountable natural obstacle between the accursed lands of the south and the populated northern lands. Flying demons, such as fian, can fly across but for an army there are only two places where such a force can easily pass. One is the high plateau of Tenra - guarded by ranwulf barbarian hordes and humans at the great terraced fortress-city of Tenra itself that straddles the narrowest point of the pass up onto the plateau from the south. The other place is via the Dragon Mountains, through dragon-infested Nerat and then on through the Valley of the Dead; one of two places were the Spirit World is close to the land of the living and the undead walk here freely and will destroy anything, demons included, that violate this place held sacred by the Lord of the Dead. Even if any demons survived that place, they would have the Scorpion Swamps to contend with and the vast Ancient black dragon Ishmilnark and his minions. The dwarf tunnels through the mountains are another option, but they are not practical for getting an entire army through since there are Elder things from the Lower Planes that sleep in the depths of those caverns that even a chaos demon army would be ill-advised to disturb with their passing. Small groups and many individual demons make it through, but an army would, most likely, not.
The presence of the demons and the Dreaming Gate have damaged the surrounding land (hence the name: 'Ruined Land') and so the plain of Azoth is a barren, desolate place where little grows. There is much volcanic activity with many hot springs and brimstone-stinking vents and the only safe drinking water come from the river that runs from the vast Sour Water Lake.