There are a total of 19 castles along the Wall. 19 castles or fortresses.
But no more than 17 were ever in use at any one time.
There were points in history where they would build a new castle
and then they would abandon one of the old ones.
So I believe 17 was the most that were ever being manned simultaneously.
But there are still 19 structures there.
But at the present day,
there are only three in use.
Castle Black in the center, Eastwatch to the east by the sea,
and the Shadow Tower, which is up in the western mountains.
Those are the three that are still in use.
The Nightfort, which is one of the abandoned castles,
is very old.
It may have been the original castle on the Wall.
So there's a lot of legends around the Nightfort.
Many of them, very dark legends, because in the history of the Watch
which, at least by tradition, goes back, like, 8,000 years,
some very dark things have happened,
and a lot of those things have happened at the Nightfort.
But right now it's just this large, crumbling ruin,
which they decided to abandon simply because of its size.