Karsoluthiyl

Karsoluthiyl was a drow city located beneath the Trackless Sea, west of the mouth of the River Chionthar.

Two prominant houses were House Tanor'Thal and House Lysaen. Both houses were big players in the slave trade of Skullport.

Geography
Karsoluthiyl is located in a region of the Underdark known as the Swordsea Depths, which lies underneath the Sword Coast. They are engaged in a struggle for supremacy with Aboleths, Svirfneblin, and Thaalud who also call the area home.

It is connected by long and arduous tunnel routes to Undermountain to the north, Sshamath to the east, and the realms of Deep Shanatar to the south. In addition it is at the end of a series of portals which link from Karsoluthiyl to sea caves in Ruathym, from there to caverns in the Crags near Neverwinter, to the Undermountain, another set of caves in Ruathym, and back to Karsoluthiyl.

History
Although some claim that Karsoluthiyl was founded by House Tanor'Thal in −105 DR, the Year of the Bloody Goad, Drow from the city were identified as being at war with Clan Melairkyn as early as −677 DR (Year of Fervent Glances). The war was sporadic until the Drow attacked in force in 34 DR, bypassing the dwarven defenses through magical disguise, levitating up Belkram's Shaft, and killing Melair IV, the last king of Melairbode. They proceeded to re-purpose the dwarven halls to their own needs, building up the outpost of Kyorlamshin, and even building a barracks and martial academy, the Citadel, and the Crystal Labyrinth. Their success was only to be short lived as Halaster's arrival in the Undermountain precipitated Halaster's Hunts which started in 171 DR and ended with the Drow withdrawing completely from the Undermountain by the Year of the Ecstatic Priest, 493 DR. During this time many Drow were also captured and twisted by Halaster's apprentice Murial into "Murial's Creations".

A series of Drow raids occured along the Sword Coast and resulted in the destruction of the small kingdoms of Harpshield and Talmost. The Drow were unidentified, but given the location it seems reasonable to suspect Karsoluthiyl. Drow in the area also attempted to excavate the Netherese ruins of Philock. Philock lies in the tunnels between Karsoluthiyl and Sshamath. In 1163 DR the Jaezred Chaulssin returned from the Plane of Shadow to the Prime Material Plane and established a fosterage in Karsoluthiyl among other cities. This fosterage went under the guise of the wealthy merchant House Oussghym. At least two centuries later the house was led by Patron Father Quildan Oussghym, and had developed a rivalry with House Lysaen. Karsoluthiyl was one of the cities in which the Jaezred Chaulssin were able to weaken the power of the matriarchy during the Silence of Lolth.

At some point the Drow re-established links with the Undermountain, being heavily involved in the slave trade in Skullport, as well as competing with Duergar to sell Deep Rothé meat and hides. House Tanor'Thal dominated the trade from Karsoluthiyl due to their control over the portal system. Their interests there were great enough for Matron Mother Haelra Tanor'Thal to send her niece Kesra to act as de facto Matron Mother in Skullport, and building a massive spider shaped compound. House Lysaen attempted to establish their own presence, under the guidance of Ahlysaaria Yril'Lysaen but they were forced to travel a long physical route, part of which was above ground through the Forest of Wyrms, presumably to stop at the ruins of Tholhtzin where the Serpentfolk of Najara purchase slaves. Other threats included Malakath Tabuirr, head of the Dark Dagger who originally hailed from Karsoluthiyl. His house was destroyed by House Tanor'Thal and he escaped, changing his name to Tabuirr. He used his position and organization to secretly undermine House Tanor'Thal's commerce by attacking their caravans.

During the Spellplague much of Skullport was destroyed, and described as being only home to houseless Drow, suggesting that much of the various Karsoluthiyl interests were no longer operating.