Main Headquarters of The Dawnguard, Fort Dawnguard was originally just a fortified keep in the mountains southeast of the city of Riften. After the Volkihar Conflict, a number of individuals rallied to the fort to enlist as Vampire Hunters. Agriculture, Industry, and Infrastructure needs quickly arose, to supply such a place, and with the needs of the city of Riften not allowing for much to spare for another settlement, new people moved to the area and began building up a town around the fort.
Due to some losses during the Third Great War, Honorhall Orphanage was also taxed in its abilities. So a new orphanage was built in the area and officially began the life of a new official city of the Rift. Furthermore, in the interest of supplying more arms and armor for the members of the Dawnguard, a nearby mine was expanded until it uncovered a new passage into the realms of Morrowind, opening up a new road through the area of the fort to connect The Rift to The Grey Meadows in Morrowind, via the city of Kogotel.