Twthill (Welsh: Twtil) is a Norman castle located near the town of Rhuddlan, Denbighshire in Wales.
Twthill castle is built to a ‘motte and bailey’ design and was erected by Robert of Rhuddlan in 1073 at the command of William the Conqueror to consolidate Norman advances into the north of Wales.
It remained in use for two hundred years until Rhuddlan Castle was built, adjacent to Twthill, on the orders of Edward 1. Tradition has it that Twthill Castle was built on the site of Gruffydd ap Llywelyn’s palace.
Only the Motte mound remain today to the south of Rhuddlan Castle, standing 12 metres high with a maximum diameter of 80 metres, although impressions of the Bailey can been seen in the surrounding fields. Much of the site has degraded due to the sandy soil conditions.
Twthill may sometimes appear in maps or documents with the alternative names of Toothill or Tot Hill.
It is currently in the care of Cadw and is open to the public.