From PathfinderWiki

The massive, rune-covered wheel of Gruankus lies half-buried on the shore of the Varisian Gulf. Presumably a Thassilonian artifact, its original purpose remains unknown, much the same as the Cyphergate in Riddleport to its east. It was the location of the signing of the Treaty of Gruankus between the pirates of Riddleport and the leaders of Magnimar, nearly a hundred years ago, ostensibly to reduce the danger of piracy to traders travelling the Varisian Gulf.[1][2][3]