APA (7th ed.) Citation

Markus, R. A. (1997). Gregory the Great and his world. Cambridge University Press.

Chicago Style (17th ed.) Citation

Markus, R. A. Gregory the Great and His World. Cambridge ; New York: Cambridge University Press, 1997.

MLA (9th ed.) Citation

Markus, R. A. Gregory the Great and His World. Cambridge University Press, 1997.