Criccieth Castle was built by Llywelyn ap Iorwerth (Llywelyn Fawr) before 1239. “Apparently, Criccieth’s castle was built at the beginning of the 13th century, a rather late date for initiating a castle at a particular site in Wales. The earliest mention of a stronghold on the craggy outcrop is to be found in the Welsh chronicles, the Brut y Tywysogyon, in the year 1239, when Gruffydd ap Llywelyn (son of Llywelyn ap Iorwerth, or “the Great”) was imprisoned in the castle by his half-brother, Dafydd. Most likely, Llywelyn the Great began the stone fortress just a few years before his sons’ quarrel.” http://www.castlewales.com/criccth.html
Llywelyn kept Gruffydd here and then upon Llywelyn’s death, so did Dafydd, Llywelyn’s son and Gruffydd’s half-brother. Gruffydd was transferred to the Tower of London as part of a deal with the King of England, as a way to control Dafydd and prevent him from waging war against the Normans. When the rope by which Gruffydd was attempting to escape the tower broke, Dafydd began his war again.
The castle was augmented first by Llywelyn’s grandson, Llywelyn ap Gruffydd, and then by Edward I after the Norman conquest of Wales.
“The inner bailey contains some of the earliest building, including the inner gatehouse with its two, semi-circular towers, the south east tower and the inner curtain wall. As was usual, substantial alterations and necessary repairs were carried out during the 14th century and it is, therefore, quite difficult to distinguish much of the original work, especially as the site is now largely ruinous.
However, the majority of the inner curtain wall stands almost to its full height and, along parts of it, the original wall walk remains. The south gate, a former entrance to Criccrieth Castle ‘on foot’, served as access between the inner and outer baileys, when the outer bailey was constructed towards the end of the 13th century. The outer gatehouse was once a passage through the curtain wall with an internal gate, but an outer gate was later added and a simple barbican built to provide extra defence.
Prior to the Edwardian conquests, it is likely that the living quarters at Criccieth Castle were in the south west tower overlooking the sea, and the large, square north tower (Engine Tower) possibly supported an engine – such as a catapult – on the roof. Although there is little actual ‘castle’ left to explore, having hiked to the top of this grassy headland, the visitor will not fail to be impressed by the spectacular views across Tremadog Bay.” http://www.theheritagetrail.co.uk/castles/criccieth%20castle.htm