Denys Hay, Annalists and Historians: Western Historiography from the Eighth to the Eighteenth Centuries (London/New York) 1977.
Sigebert of Gembloux (Patrologia Latina, CXL, 584 sq.) calls him also Bishop of Vercelli, but the early documents of the diocese leave no place for him in the list of bishops.
For the years previous to 1181 this is merely a compilation from Prosper of Aquitaine, Sigebert of Gembloux and others, but it is an original authority for the period from 1181 to 1211.