Trim Castle is the largest Cambro-Norman castle in Ireland. The castle interior was partially the subject of an archaeological dig by David Sweetman of OPW in the 1970s and more extensively by Alan Hayden in the 1990s. the Dublin gate was erected in the 1190s or early part of the 13th century; and the remaining wall to the south with its round towers dates to the first two decades of the 13th century. The castle has two main gates. The one in the west side dates to the 1170s and sits on top of a demolished wooden gateway. The upper stories of the stone tower were altered to a semi-octagonal shape, c. 1200. The Dublin Gate in the south wall is a single round towered gate with an external barbican tower. It dates from the 1190s or early 13th century and was the first example of its type to be constructed in Ireland.