King John’s Castle, on the south side of Thomond Bridge head, built in 1210 “to dominate the bridge and watch towards Thomond”, is one of the finest specimens of fortified Norman architecture in Ireland.
The castle is roughly square on plan and its 60 meter frontage along the river is flanked by two massive round towers, each over 15m. in diameter with walls 3 metres thick. The castle gate entrance – a tall, narrow gateway between two tall, round towers is quite imposing. There is another massive round tower at the north east corner of the fortification, but the east wall and the square tower defending the south-east corner of the castle, and on which cannons were mounted, is long demolished.
There was a military barracks erected within the walls in 1751, some of which still remains. Houses were also erected in the castle yard at a very much later date. These have now been removed and a modern visitor centre built on the walls.
The walls and towers still remaining of the castle are in reasonably good state of preservation. The domestic buildings of the courtyard do not survive, except for remnants of a 13th century hall and the site of what could be the castle chapel.