Of the old castle, called Nenagh Round, dating from the time of King John, there still exists the circular donjon or keep. There are no remains of the hospital founded in 1200 for Austin canons, nor of the Franciscan friary, founded in the reign of Henry III.
Other published correspondence is Lettres de Mirabeau a Chamfort (1796); Lettres du comte de Mirabeau b Jacques Mauvillon (Brunswick, 1792); Lettres originates de Mirabeau, ecrites du donjon de Vincennes, 1777-178Q, published by L.
The chief buildings are the chateau, mainly of the 15th century, of which the massive donjon of the 11th century known as the Tour de Cesar is the oldest portion; and the abbey-church of Notre-Dame, a building in the Romanesque style of architecture, frequently restored.
The nucleus of the stronghold is a donjon over 200 ft.
This tower formed part of the donjon of the fortress erected by Baldwin IV., count of Hainaut, about the year 1150.