The earliest known surviving castle is in the Loire Valley in northern France at Doué-la-Fontaine (Maine-et-Loire), dated to ca. 950, while the second oldest occurs near by at Langeais at the close of the same century. Both appeared at precisely the time and place where feudal society itself originated. Langeais is attributed to Fulk Nerra (the Black), Count of Anjou (reigned 987-1040), 'a pioneer in the art of feudal government' (R. Southern) and a mighty builder of castles, who used them, manned by his knights and vassals, to create and develop his feudal principality. The chateau was rebuilt about 1465 during the reign of King Louis XI. The tall fortified hall at the rear of the enclosure is thought to be among the earliest datable stone examples of a keep (donjon) in Europe.