Thurd was a green martian city, enemy of the Torquasian horde. A remnant of an interplanetary expedition of antediluvian date survives in the local wilds and has of late joined with the red apemen and their beast-slaves to menace the defenseless villagers.
Who will stop them? You, and your pallid flabbiness and your rakes and sharpened sticks?
(This is just some half-assed mood setting for my next sesh--but do feel free to read it as political allegory--uh, but it doesn't really match up to anything.)
Here's a Thark as drawn by Mahlon Blaine: