Long Barrow is one of the abandoned castles of the Night's Watch, standing on the Wall between Rimegate and the Torches, west of Eastwatch-by-the-Sea. Its name is old as the First Men, recalling the barrows in which they laid their dead.
The Eastern Marches
The castles of the eastern Wall were emptied as the Watch withered, their brothers drawn back to Eastwatch and Castle Black, and Long Barrow stood among the forsaken. Its keeps endure, weathered but unbroken, and of the empty castles of the east it is reckoned among the fittest to hold a garrison again, should the Watch ever find the men to fill it.