 Llywelyn the Great initially controlled the princedom of Gwynedd , but grew more powerful over the course of his reign , extending his influence over much of Wales during the early years of the 13th century . Llywelyn was faced by several challenges , including dealing with the threat from the kings of England , and maintaining his authority over the native Welsh . As part of this strategy , Llywelyn built Castell y Bere , an innovative stone Welsh castle , in the 1220s . Shortly afterwards he began the first phases of Dolbadarn Castle , constructing the initial stone fortifications on the site , including two square stone towers . 
