Acheron covered an area roughly corresponding to Aquilonia, Argos and Nemedia, and its dominion later extended over western Koth, Ophir, and Corinthia. The latter three nations were under the hegemony of Old Stygia, apparently falling to Acheron at a later date. It is likely that Acheron overextended itself by annexing these Stygian satellites, leaving its northern frontier vulnerable to the subsequent Hyborian invasions.
Not much is known about the chronology of Acheron; but it seems to have flourished for about 2,500 years as a theocracy under the control of necromancers and wizards. The barbarian pressure of the more vigorous Hybori came down from the north and ultimately destroyed Acheron. Its demise took place 3,000 years before the time of Conan.
The wizard Xaltotun attempted to restore the ancient kingdom, but was stopped by Hadrathus, a priest of Asura, and Zelata, a witch, with the power of the Heart of Ahriman. According to the Conan tale featured in Marvel Comics, the Hyborean Age was littered with remnants of the Archeron Empire, from relics to lost cities.