APA (7th ed.) Citation

Gregor I. Papst 542-604 & Martyn, J. R. C. (2004). The letters of Gregory the Great. Pontifical Institute of Mediaeval Studies.

Chicago Style (17th ed.) Citation

Gregor I. Papst 542-604 and John R. C. Martyn. The Letters of Gregory the Great. Toronto: Pontifical Institute of Mediaeval Studies, 2004.

MLA (9th ed.) Citation

Gregor I. Papst 542-604 and John R. C. Martyn. The Letters of Gregory the Great. Pontifical Institute of Mediaeval Studies, 2004.