From A Wiki of Ice and Fire
The Jade Gates is a narrow strait which connects the Summer Sea and the Jade Sea, separating the great city of Qarth on the southern coast of Essos from the island of Great Moraq. The Cinnamon Straits is a similar passageway south of Great Moraq. Located in the east of the strait is the small island of Qal, which is fortified at each end with Qartheen harbor cities.
The Jade Gates is a major trade hub between the east and west from which Qarth derives its considerable wealth and power by taxing passing ships. The strait is patrolled by the ornate galleys of the Pureborn of Qarth.