Much of Criccieth, as it can be seen today, came into being with two major innovations in communication. The first of these was the turnpike road running from Tremadog to Porthdinllaen, the proposed principal harbour for Ireland, in 1807, and the second, the railway in 1868, which placed the town on the map as a Victorian seaside resort.

However, from far further back in history, come the two main sites in Criccieth, the castle and the church. They are situated at a surprising distance from each other, one third of a mile, thus suggesting perhaps that the foundation of each was originally unconnected.

It is quite possible that in prehistoric times a fort was built on the castle mound or on the Dinas nearby, but nothing apparently remains. However, the first written reference to the stone castle was in 1239; it was probably built in 1230 by Llywelyn Fawr who had been in control of the area since 1202. At this time the administrative centre of the commote of Eifionydd was moved from nearby Dolbenmaen to the newly built castle at Criccieth.