28 November – Saint Gregory III

Modern Hagiography

Bibliotheca Sanctorum

Martyrologium Romanum (10 December)

Roman Martyrology

Lives of the Saints by Sabine Baring-Gould.

Medieval Hagiography

BHL

Liber pontificalis

Art & Architecture

Supposed Medallion of Pope Gregory III, but look at this selection of papal coins from the 8th through 10th centuries and a coin of Emperor Leo III issued by Pope Gregory III (see also)

Catalogo generale dei beni culturali

Portail Biblissima

Saints and their Emblems