Catholic Encyclopedia
Pope St. Caius, d. 296 after twelve years as bishop of Rome.
For All the Saints
Short essay on what little we can know about Pope St. Caius.
Popes Through the Ages
Short biography of Pope St. Caius, from the book by Joseph Brusher.
The Ecole Glossary
Brief article on Pope St. Gaius, by Karen Rae Keck.