Twthill (Welsh: Twtil) is a Norman castle located near the town of Rhuddlan, Denbighshire in Wales; historic names for the site include Toothill and Tot Hill Castle and it is also known as Old Rhuddlan Castle. It is a motte-and-bailey castle and was later replaced by the much larger, stone-built Rhuddlan Castle. The only remaining visible signs of the old castle are the large mound of the motte, and traces of the wall that surrounded the bailey.