|The information in this article comes from Dynamites, Warriors of Mars and is not written by Edgar Rice Burroughs.|
Seth was a beautiful and powerful red martian city before its destruction. It was led by the Jeddak Hath, and was the home to Dejah Thoris' mother Heru. The city is right upon a Canal so it is fairly fertile. The people of Hath are enemies of the Thither people, the thither plot against them and even kidnapped the Jeddaks Daughter. This city was where Gullivar arrived when he first set foot on mars, and when Heru was abducted by the Thither Gullivar fought them!
After Gullivar saved the princess Heru the Thither launched an assault on the city. The city was destroyed, Gullivar was seemingly killed in the battle, as was the leaders of the two peoples Hath and Ar-Hap.
Seth is from Edwin Lester Linden Arnold's "Lieutenant Gullivar Jones: His Vacation" (more commonly known as Gulliver of Mars). This book predates Burroughs martian series, but never achieved nearly the same popularity.