Dún Dealgan Motte, Medieval motte-and-bailey castle in Dundalk, Ireland

Dún Dealgan Motte is a Norman motte-and-bailey earthwork northwest of Dundalk, on a ridge above the Castletown River. Its flat-topped mound measures about 68 m across at the base and 10 m high, with a bailey to the southeast. A castellated tower, Byrne's Folly, stands on the summit.

The castle was founded in the late 12th century by Bertram III de Verdun and served as a stronghold under Hugh de Lacy. It was abandoned around 1210 when King John's forces took control of the region.

Legends name the mound as the birthplace of Cú Chulainn, and in the Táin Bó Cúailgne he bases himself here. The Annals of the Four Masters record a battle at the site in 500 AD. The hill was called Dealga at first, with dún added after 1002.

The climb to reach the castle site takes about 5 to 10 minutes on foot using stone steps and climbing over a stone fence. The ground is open terrain, so visitors should be prepared for walking uphill on uneven surfaces.

Beneath the mound runs a Z-shaped souterrain tunnel roughly 17 meters long, built during the Gaelic period long before the medieval castle. This hidden underground passage reveals layers of occupation and defense strategies across different eras.