Modern Hagiography
Lives of the Saints by Alban Butler.
Lives of the Saints by Sabine Baring-Gould.
The Liturgical Year by Dom Guéranger.
Medieval Hagiography
The Golden Legend (and illustrations)
Art & Architecture
Catacomba di Ponziano (Santi Abdon e Sennen) (more info, catacomb painting)
Warburg Institute Iconographic Database
Medieval Religion Listserv – Dillon 2016.
Nihil sub sole novum 