When on the Prime Material plane, Zanassu (in truth, Selvetarm) ruled over the evil creatures of Spider Swamp in Calimshan and kept many of the leaders of Volothamp (a nearby city) in his thrall.
In 290 DR, Zanassu was summoned by some of the aranea of the Spider Swamp, who were desperate for aid against Empress Shoon V, who (wrongly) blamed them for a plague that had fallen on Almraiven and was seeking to annihilate their race. These aranea embraced Zanassu's dark power, and two years later, he led them in battle against the capital of the Shoon Imperium itself. However, Shoon V's magical defenses and her loyal troops defeated him, and he was banished back to the Abyss. His aranea servants retreated back to the Spider Swamp.
Lolth later schemed to eliminate Zanassu by telling Selvetarm that it would please his patron Eilistraee if he defeated Zanassu and absorbed his power. While Zanassu was still weakened by his loss against the forces of Shoon V, Selvetarm attacked and was victorious over the demon lord, but absorbing his chaotic evil–tainted power tipped the balance in Selvetarm to the side of evil.
The aranea of the Spider Swamp were unaware of these happenings on another plane of existence, and for at least the next millennium, a subsection of the aranea continued to worship Zanassu, oblivious to the fact that they were truly serving Selvetarm.
By 1370 DR, the fewer than 100 priests and worshipers of "Zanassu" had established an elaborate temple for him in the settlement known as Lost Ajhuutal in the center of the Spider Swamp. This stone temple had a dome in the shape of a great spider, a minaret at each corner of the courtyard, and stone webbing extending from the central dome to each of the minarets. The temple of Zanassu was well defended, and because it also protected the non-evil aranea living below the ruined city, these evil aranea were tolerated.
- ↑ 1.0 1.1 1.2 1.3 Scott Haring (1988). Empires of the Sands. (TSR, Inc), p. 61. ISBN 0-8803-8539-1.
- ↑ 2.0 2.1 Eric L. Boyd (1998). Demihuman Deities. (Wizards of the Coast), p. 34. ISBN 0-7869-1239-1.
- ↑ 3.0 3.1 3.2 3.3 Steven E. Schend and Dale Donovan (September 1998). Empires of the Shining Sea. (TSR, Inc), pp. 90–91. ISBN 978-0786912377.
- ↑ Eric L. Boyd (1998). Demihuman Deities. (Wizards of the Coast), p. 12. ISBN 0-7869-1239-1.