|Calixtus I - Biographical profile of the third-century pope, in the 1911 Encyclopædia Britannica.
||Callistus (Callixtus) I, Pope - Biographical portrait.
|Callistus I - Illustrated profile, with links.
||Callixtus I - Short biography, by Karen Rae Keck. It was Callixtus who excommunicated Sabellius.
|Catholic Online: St. Callistus I - Hagiography, by Terry Matz.
||Pope Callistus I - Martyr, d. about 223. Also known as Callixtus or Calixtus.
|St. Calixtus I - This pope is known mostly through the writings of his enemies.
||St Calixtus, or Callistus, Pope, Martyr - From Butler's Lives of the Saints.
|Vietnamese Eucharistic Youth Society: St. Callistus I - The story of this pope, suited to children.