City State of the Invincible Overlord

The City State of the Invincible Overlord was the first published fantasy role-playing game campaign setting, designed for use with Dungeons & Dragons, and officially approved for use with Dungeons & Dragons from 1978 through 1983. Published by Judges Guild and later under license by Necromancer Games, the City State, or CSIO as it is also known, was first released at Gen Con IX in 1976.

The CSIO was designed by Bledsaw with the assistance of Owen, and was based on Bledsaw's own Dungeons & Dragons campaign.

The CSIO launched Judges Guild as a company, and was the centerpiece of the Judges Guild's Wilderlands of High Fantasy campaign setting, the first licensed and published Dungeons & Dragons campaign setting.

The City State has gone through several editions:

Campaign Installment I (1976), 16-page booklet. Guide to the City State (1977), 56-page booklet. Revised City State of the Invincible Overlord (1978-1980, three printings), 80-page book. Revised City State of the Invincible Overlord (1981-1983, three printings), 96-page book. Revised City State of the Invincible Overlord (1999), 96-page book. City State of the Invincible Overlord (2004), 288-page hardcover book, published by Necromancer Games.