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 . Its ruins were largely destroyed by a controversial road development completed in 2005 . History . 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 . 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 . M50 motorway and " The Carrickminders " . The ruins of the castle were the subject of a long running dispute before the M50 motorway was built through the site of the castle . It began in 2002 when activists , including Vincent Salafia and Gordon Lucas , who called themselves the " Carrickminders " camped out on the castle ' s ruins to prevent them being removed to make way for the motorway . They were joined by preservationists , including Professor Sean Duffy , Head of the Department of History at Trinity College Dublin and Dr . Mark Clinton , who was the archaeologist employed by the National Roads Authority as Site Director . They argued that the site ' s potential for historical study had not been fully realised . They questioned why the line of the M50 rerouted through the castle in 1998 when the proposed new road was originally routed around it in 1983 on the advice of a state agency ? In 2005 both the M50 motorway and the junction were completed . Supreme Court ruling . The Supreme Court , according to a report in " The Irish Times " on 26 July 2006 , unanimously upheld the constitutionality of new laws affecting the preservation of the Carrickmines Castle site . While noting that the new legislation — Section 8 of the National Monuments ( Amendment ) Act 2004 — " removes a bundle of protections " from national monuments , the five - judge court found the Oireachtas is not prohibited under the Constitution of Ireland from enacting such laws . The Court found that in issuing directions , the Minister for the Environment , Heritage and Local Government was entitled to balance the benefits of archaeological preservation against the wider public interest that would accrue as a result of the road development . Section 8 effectively provided that the works affecting the Carrickmines Castle site were to be carried out on the Minister ' s directions . Provided the Minister exercised his discretion under section 8 in a constitutional manner , he could give such directions as he thought fit , the Court found . This effectively meant that the road works at Carrickmines Castle were no longer to be regulated under the National Monuments Acts , the court said , although the castle was accepted as being a national monument and the works would mean a large part of a moat discovered at the site would cease to exist . Under section 8 , Dún Laoghaire - Rathdown County Council , as landowner , did not need consent from any statutory body for undertaking the works and Oireachtas approval was not necessary . There was also no requirement to obtain a licence under the 1930 National Monuments Act and An Bord Pleanála was precluded from considering whether proposed works were likely to have a significant effect on the environment and from directing an environmental impact statement . There was " only the requirement that the works be carried out on the directions of the minister " , the court said . It rejected claims that those directions – issued by the Minister , Dick Roche , in August 2004 – breached provisions of European Commission environmental directives and were therefore null and void . The Supreme Court was delivering its judgement on an appeal against the High Court ' s rejection in September 2004 of a challenge by Dominic Dunne , both to section 8 and to the ministerial directions . Dunne indicated that he intended to take his case to the European Court of Justice . Corruption allegations . On 26 July 2006 , the Criminal Assets Bureau successfully obtained a High Court order freezing land assets of at Carrickmines , County Dublin , owned by Jackson Way Properties Ltd and preventing their sale . The CAB contended that these lands had been rezoned on 16 December 1997 by Dún Laoghaire - Rathdown County Council from agricultural to industrial after Frank Dunlop bribed and made corrupt payments to councillors to secure their support in the rezoning vote . That vote increased the value of just of the property from €8 million to €61 million . The CAB interviewed and took statements from Frank Dunlop for use as a witness against a number of property developers . The lands in question have been the subject of investigation by The Mahon Tribunal in 2003 and 2004 .