Seis is one of the oldest cities in existence, and, although it has been sacked numerous times, has for much of its existence been among the greatest cities of the world. Located in the delta of the River Sesh, it has long been a hub for trade and finance, as well as being a religious center for most of the Seshweay faiths.

Seis rose to become a major metropolis during the Bronze Age, when it was the capital of the Empire of the Sesh. Following the Empire's collapse, Seis remained the political, cultural, and economic center of the Seshweay diaspora. It was the capital of the shortlived Union of Aya'se before its fall to the Exatai of the Satar under Arastephas.

As a Satar city, Seis was once the largest, then the second largest city of the Accan Exatai. At its height, it might have held 200,000 in the city and environs, but that number is now closer to 100,000.

After Macrinus quelled the great rebellion under Aitah, he deliberately destroyed the walls of Seis and Pa, to ensure that the overwhelmingly Seshite cities could never be held against any of his descendants were another rebellion to occur. Seis is a major manufacturing center, exporting finished goods to countless regions. While still under the rule of the Ardavai Exatai, it was the personal domain of the Princes of the Sun, the Accan descendants of Macrinus. It later was reconquered by its Seshweay founders. Nine out of every ten subjects are Seshite, but significant populations of Satar and Accans intermingle in the palace district.