Maybe you remember one of the alternative builds (ah, good times) and not the main model... I vaguely remember a bridge or something as an alternative build of one of my old castle sets.
Black Monarch’s Castle 6085 has a black horse and a draw bridge and as an alternative build a tower bridge:
Knight’s Stronghold 6059 has a bridge with superstructure as an alternative build (with a white horse)
and Black Knight’s Castle 6086 has a drawbridge and a black horse on it as one of it's detail photos
“Accept His Noodly Magnificence into your heart, into your soul, and ye shall forever be free. R'Amen.” – Ragu