The book of the popes (Liber pontificalis).
I,
To the pontificate of Gregory I,
translated with an introduction by Louise Ropes Loomis.
APA Citation
Loomis, L. Ropes. (1916). The book of the popes (Liber pontificalis). New York: Columbia University Press.
MLA Citation
Loomis, Louise Ropes, 1874-1958. The Book of the Popes (Liber Pontificalis). New York: Columbia University Press, 1916.
Warning: These citations may not always be complete (especially for serials).