The Conclave of Essia consists of representatives from all of the Essia's sovereign city-states, of which there are a bit more then three hundred. It was formed in YE 29 to represent Essia System to Yamatai. They elect by range voting a group of twelve, who are joined by the high priest of Nagashun, to represent them to Yamatai. One of the representatives is the Senator from Essia in the Senate of Yamatai. The capital is in Apollo, close to the most important temple to Nagashun.
It was originally formed by the twelve largest city-states in YE 29 to present a unified face to Yamatai. However, it was instantly opposed leading to two brief civil wars in YE 30 and YE 32. In YE 32, the conclave expanded to allow a bit more than three hundred cities in the Conclave that elect twelve members by range voting. In YE 34, Tiktal, the largest city on Ssinisa, declared itself sovereign and was admitted to the conclave.
In YE 40, during the Kuvexian invasion of Essia, some of the representatives escaped, forming a government in Exile. Two weeks later, a similar group was appointed by a new session of the conclave to be Essia's representatives to Kuvexia as their ally. However, with the liberation of Essia, nearly all of the representatives immediately reswore loyalty to Yamatai and noted that they didn't exactly have a choice about allying with Kuvexia.
Only a few things were reapproved by the Conclave, one of them being their agreement with the Freespacers.