20 April – Saint Theodore Trichinas

Bodleian Library MS. Gr. th. f. 1, fol. 036v-037r: Sts. Theodorous, Trichinas, Jannuarius, Theodorus, Georgius, Sabas, Stratelates, Marcus, Basileius
S. Théodore, confesseur (St. Theodore Trichinas, Confessor), April 20th, from Les Images De Tous Les Saincts et Saintes de L'Année (Images of All of the Saints and Religious Events of the Year), Jacques Callot (French, Nancy 1592–1635 Nancy), Etching; second state of two (Lieure)
Les Images De Tous Les Saincts et Saintes de L’Année
The Book of Saints

Modern Hagiography

Bibliotheca Sanctorum

Martyrologium Romanum

Roman Martyrology

Medieval Hagiography

Acta Sanctorum

Art & Architecture

Agios Theodoros Trichinas in Fortezza, Crete

Caractéristiques des saints dans l’art populaire by Charles Cahier – ermitage, possédés.

20 April – Saint Theotimus

Saint Théotime (France, Paris. Bibliothèque nationale de France, Département des manuscrits, Grec 923 f.279)
The Book of Saints

Modern Hagiography

Bibliotheca Sanctorum

Roman Martyrology

Lives of the Saints by Sabine Baring-Gould.

Our Birthday Bouquet Culled from the Shrines of the Saints and the Gardens of the Poets by Eleanor C. Donnelly.

Pictorial Half Hours with the Saints by Auguste François Lecanu.

Medieval Hagiography

Acta Sanctorum

The Cult of Saints in Late Antiquity Database

Sozomen, Ecclesiastical History

Art & Architecture

Index of Medieval Art

Portail Biblissima

Saints and their Emblems

20 April – Saint Marcellinus of Gaul

Saint Marcellinus’s Journey from Africa on a Capital at the Prieuré de Chanteuges (better photo)
Tableau : le Christ en croix, la Vierge, saint Eloi, saint Marcellin d’Embrun et un donateur, vue générale (perhaps also in the panel)
The Book of Saints

Modern Hagiography

Bibliotheca Sanctorum

Martyrologium Romanum

Roman Martyrology

Lives of the Saints by Sabine Baring-Gould.

Character Calendar

Pictorial Lives of the Saints

La vie des saints 

Medieval Hagiography

BHL

Acta Sanctorum

The Cult of Saints in Late Antiquity Database

Art & Architecture

Index of Medieval Art

POP : la plateforme ouverte du patrimoine

Église Saint-Marcellin du Prieuré de Chanteuges – Wikimedia Commons, Flickr Gallery

Saints and their Emblems