Graht-oaks were enormous trees in the Imperial province of Valenwood, the homeland of the Bosmer, or Wood Elves as they were known to many Imperials. They were allowed to move by powerful magicks being cast in the Mythic Era. Gnarled and twisted, graht-oaks had golden and green leaves, and were covered with sap. They were approximately a mile long and a half-of-a-mile wide, allowing the Bosmer to build cities within and on them such as Falinesti.
The Bosmer carved their homes into the graht-oaks and built natural homes out of the branches and leaves in the boughs. Each branch or bough was a distinct district, such as Havel Slump in Falinesti, of the city.
In the Fourth Era, the graht-oaks stopped walking and rooted themselves for the first time in recorded history.