Undrek'Thoz was a confederation of drow cities, called segments, beneath Thay. The ten cities that comprised Undrek'Thok were spread across the Middledark, each connected to the others by way of Portals. The Matron mothers that ruled were kept in check by a monastic order known as the Blackened Fist.

Originally the far flung segments of Undrek'Thok were all independant drow cities, spread throughout the eastern Middledark. In 114 DR, the drow sent representatives from the various segments and concluded that they should band together for mutual protection, this took the form of a web of Portals that connected each city.

Over the intervening two hundred years, the cities Mezrylornyl and Sshurlynder joined the web, further increasing the power of the greater Undek'Thoz metropolis.