Modern Hagiography
Lives of the Saints by Alban Butler – Soter & Caius.
The Liturgical Year by Dom Guéranger.
Medieval Hagiography
The Cult of Saints in Late Antiquity Database – Soter, Caius
Liber pontificalis – Soter, Caius
The Golden Legend (Pope Caius)
Breviarium Romanum – Latin & English
Writings by Saint Soter
Writings by Saint Caius
Art & Architecture
Index of Medieval Art – Soter, Caius
– El Escorial, Real Biblioteca, Cod. Vitrinas 17, folio 5r & 5v:
Catalogo generale dei beni culturali – San Caio, San Sotero
BeWeB – San Caio, San Sotero
Portail Biblissima – Saint Caius and also
The Sistine Chapel, North Wall
The Saints in Art by Joseph Maria von Radowitz – Caius.
Nihil sub sole novum 
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