Complex sentence: This castle was intended to supplement or replace the first castle at Twthill, sometimes referred to as the Old Rhuddlan castle, which had been fought over by the Earl of Chester and the princes of Gwynedd.
Split into simpler sentences: This castle was intended to supplement or replace the first castle at Twthill, sometimes referred to as the Old Rhuddlan castle. The Old Rhuddlan castle was much fought over by the Earl of Chester and the princes of Gwynedd.