Henry William Carless Davis, 1911 Encyclopædia Britannica, Volume 28… (1911)
“ This severity to a man who was generally thought innocent, is one of the dark stains on his career. In 1076 he invaded Brittany to get possession of the fugitive earl of Norfolk; but Philip of France came to the aid of the Bretons, and William gave way before his suzerain. The next few years were troubled by a quarrel between the king and his eldest son. Robert fled from Normandy and after aimless wanderings obtained from King Philip the castle of Gerberoi, in the Beauvaisis, from which he harassed the Norman marches. ”
