Carrickmines Castle

Carrickmines Castle is an archaeological site in Carrickmines, County Dublin, in eastern Republic of Ireland. The castle was built in the Middle Ages to protect the English-ruled Pale around Dublin. The mostly subsurface ruins lay in the path of the M50 Motorway, completed in 2005. Sections of the medieval walls and some sections of the castle's defensive structures were preserved within or under M50 roundabouts.

Carrickmines Castle was the site of an Hiberno-Norse settlement which during the 12th century became a fortified Norman castle and village, on the frontier between Dublin and Wicklow, Ireland. Guarding the southern plains, this fortress was once a central medallion in the necklace of the Norman castles and outposts dotted along the outskirts of The Pale – the area around Dublin under English rule during the medieval period.

In 1402 the O'Byrne clan of County Wicklow, who periodically raided Dublin, moved a large mercenary force to the banks of the River Dargle at Bray, but, as the direct route to the city would bring them close to the stronghold of Carrickmines, they apparently hesitated before attacking. The delay allowed the Walsh family, who owned Carrickmines, to send an urgent warning to Dublin. The Dubliners responded decisively: the Mayor of Dublin with a large force fell on the O'Byrnes and defeated them, in an encounter popularly known as the Battle of Bloody Bank, due to the number of casualties.

As a major fortress, it had an extensive curtain wall flanked by towers protecting an area of some acres. Within this was settlement with a variety of wooden and stone buildings, mills, and a keep or hall house in the centre. The site still contains impressive defences, hewn into bedrock, and human remains from when the castle was overwhelmed in 1642.

In the Irish Rebellion of 1641, the Catholic Walshs who owned the Castle sided with the native Irish and the Confederate attempt to create the first independent Irish parliament. They paid dearly – as a focus of the Irish Confederate Wars, the Castle was besieged by English forces, and when it was retaken over 300 of the Walsh, O'Byrne, and O'Tooles were massacred.

...
Wikipedia