Lomax, John (18 October 2013). "Constance (1154–1198)". In Emmerson, Richard K. (ed.). Key Figures in Medieval Europe: An Encyclopedia. Routledge. pp. 153, 154. ISBN 978-1-136-77519-2. Retrieved 15 September 2024.
cambridge.org
Müller-Mertens, E. (2000) ‘The Ottonians as kings and emperors’, in T. Reuter (ed.) The New Cambridge Medieval History. Cambridge: Cambridge University Press (The New Cambridge Medieval History), pp. 231–266.