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The Flanaess is the eastern part of the continent of Oerik, one of the four continents of the fictional world of Oerth in the World of Greyhawk campaign setting for the Dungeons & Dragons fantasy roleplaying game. The Flanaess has been the setting of dozens of adventures published between the 1970s and 2000s and continues to be the central focus of the campaign world.

In late 1972, Dave Arneson demonstrated a new type of game to a group of gamers in Lake Geneva, Wisconsin, including game designer Gary Gygax. Gygax agreed to develop a set of rules with Arneson and get the game published; the game eventually became known as Dungeons & Dragons. Gygax designed a set of dungeons underneath the ruins of Castle Greyhawk as a testing ground for new rules, character classes and spells. In those early days, there was no "Flanaess"; the world map of "Oerth" was developed by Gygax as circumstances dictated, the new cities and lands simply drawn over a map of North America. Gygax and his friend Rob Kuntz further developed this campaign setting, and by 1976, the lands within a radius of 50 miles had been mapped in depth, and the lands within a radius of approximately 500 miles were in outline form. In addition, more distant lands had been roughly sketched out to accommodate various adventures. (For more information about the first days of Gygax's home campaign, see Greyhawk.)

Following yet more work, in 1978 Gygax agreed to publish his world and decided to redevelop Oerth from scratch. Once he had sketched out the entire planet to his satisfaction, one hemisphere of Oerth was dominated by a massive continent called Oerik. Gygax decided to concentrate his first efforts on the continent of Oerik and asked TSR's printing house about the maximum size of paper they could handle; the answer was 34" x 22" (86 cm x 56 cm). He found that, using the scale he desired, he could fit only the northeast corner of Oerik on two of the sheets. This corner of Oerik became known as "the Flanaess", so named in Gygax's mind because of the peaceful people known as the Flannae who had once lived there. Gygax also added many more new regions, countries and cities, bringing the number of political states to 60:

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