Carrickfergus Castle was begun by John de Courcy in 1177.

De Courcy was an Anglo-Norman knight who came to Ireland at the behest of Dermot MacMurrough, King of Leinster, who sought the English King Henry II's help in becoming King of Ireland.

With no inheritance in England due, no lands and title - de Courcy set off from the southeast of Ireland to the north, and effectively defeated any opposition in County Down and County Antrim. Thus begins a turbulent millennium of English involvement in Ireland.