Greencastle (Northburgh) Ango Norman Castle was built in 1305 by the powerful Anglo-Norman Richard de Burgo, 2nd Earl of Ulster, also known as The Red Earl.
At the time he had much of Ireland under his control except for the Inishowen Peninsula and Tir Connail.
These remained the territory of the O’Donnell’s and the O’Doherty’s thanks in large part to help they received from Scotland. The Earl built Northburgh right at the mouth of Lough Foyle for two main reasons.
The first was to guard the entrance to the Lough from potential invasion from Scotland and the second was to subdue the O’Donnell’s and reduce their influence in the north-west.