The water-filled trench around a castle is called a moat.
I think that the 'trench' you are thinking of is a moat. You could say that it is a trench full of water that surrounds the castle. If you are not thinking of a moat then I am sorry.
A moat surrounded the castle.The moat was a form of defence for castles.
Into the Moat was created in 2001.
Advantage of a water moat
Ryan Moat's birth name is James Ryan Moat.
The moat cleaners. ;)
The moat is filled with sharks
Ryan Moat is 5' 9".
A moat is a body of water that circles a castle, and a drawbridge is part of the castle that lowers to allow people to cross the moat.
Farther of jamie moat he is, as the sun people call him, "a"
some animals use a moat