Mamon (Aktemto in the NES version) is a small mining town in Dragon Quest IV. When Estark was sealed into slumber and entombed by the humans, Mamon was built over his tomb to keep him from ever being released. However, over the centuries he was forgotten, and the inhabitants of the town began to mine beneath it. Eventually they started to approach the lower catacombs and unknowingly released a miasmatic gas that emanated from the tomb and up the shafts and started poisoning the villagers, slowly killing everybody one by one. Over the course of the game, the townspeople become fewer, the graves become more numerous and all the buildings fall into a state of disrepair.
The party returns a number of times in Chapter 5, notably when the miners accidentally dig all the way down to Estark's tomb and unseal it, awakening him. The Hero and his companions go down to battle and kill Estark, narrowly avoiding unleashing the dangers of the Secret of Evolution on an unsuspecting world.
Despite the problem being solved, Mamon is too far gone to be saved, and eventually fades into nothing.