The Errethur Sea is a region in the Fulgent with several habitable systems. It is the primary setting of Sidereal Wars with most of the known polities being based there. It is bounded by the Maelstrom, the Patroia Rift, and the Ketarri Escarpment. The primary route out of the Sea is through the Yerra Transverse, a dense bundle of strings that leads to the Lunagia Frontier, a wild region undergoing colonization by the Republic of Erkas, the Aggosian Empire, and the Rekati Hegemony.