This imposing fortress, likely constructed by the Earl Marshall in the early thirteenth century, features a distinctive architectural layout with a large central keep flanked by circular angle towers, though only the northern tower survives intact today. The castle’s extensive defensive works include an inner ward with its own gateway and a large outer ward measuring approximately 60 by 75 metres, protected by a formidable twin-towered gatehouse added towards the end of the thirteenth century.

The castle’s turbulent history reflects centuries of conflict over this strategic crossing point of the River Barrow. Initially passing from the FitzGeralds to William Marshall, Earl of Pembroke, in 1203, Lea became a contested stronghold that witnessed numerous sieges and changes of ownership. In 1315, Edward Bruce burnt the castle during his campaign through Ireland, whilst the O’Connors, O’Mores, and O’Dempseys repeatedly attacked or captured it throughout the medieval period. The fortress played a crucial role during the Geraldine rebellion of 1535, when it served as a repository for ordnance and supplies. Its military significance continued through the Confederate Wars of the 1640s, changing hands multiple times between Parliamentarians and Confederates until Colonel Hewson’s forces deliberately destroyed two-thirds of the structure with gunpowder in 1650 to prevent its future use.

Today’s ruins reveal the castle’s sophisticated design, with the remaining structures showing walls averaging three metres thick in the keep and defensive features including a nine-metre-long entrance passage through the gatehouse. Archaeological evidence, including a window with trefoil pointed heads in the west wall, suggests modifications around 1250, whilst earthworks of unknown date surround all but the northern side of the castle. The site forms part of a broader medieval landscape, with a church and graveyard located 380 metres to the southeast and the remains of a deserted medieval settlement in the fields immediately south of the castle, painting a picture of what was once a thriving Anglo-Norman community along this important river crossing.