18 July – Saint Frederick of Utrecht

Bust of Saint Frederick, Elias Scerpswert, 1362
S. Frédéric, évêque et martyr (St. Frederick, Bishop and Martyr), July 18th, 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

Sanctorale Catholicum

Lives of the Saints by Alban Butler.

Lives of the Saints by Francis Weninger.

Lives of the Saints by Sabine Baring-Gould.

Medieval Hagiography

BHL 

Acta Sanctorum

Art & Architecture

Index of Medieval Art

Warburg Institute Iconographic Database 

Saints and their Attibutes

Medieval Religion Listserv – 2016 Dillon.

A cycle in stained glass in Quimper Cathedral 

Lives and Legends of the English Bishops and Kings, Mediaeval Monks, and Other Later Saints by Mrs. Arthur Bell.

Emblems of Saints by Which They Are Distinguished in Works of Art by F. C. Husenbeth.

18 July – Saint Bartholomew of Braga

Brother Bartholomew of the Martyrs, bishop of Braga, by António André (1618-25). Museu de Aveiro, Portugal
D. Fr. Bartholomeu dos Martyres, arcebispoprimaz de Braga 

Modern Hagiography

Bibliotheca Sanctorum

Lives of Some of the Sons of St. Dominic, First Series by Thomas Austin Dyson.

Early Modern Hagiography

Life of Dom Bartholomew of the Martyrs by Venerable Louis de Granada.

18 July – Saint Arnulf of Metz

Miracle de saint Arnoul (France, Paris. Bibliothèque nationale de France, Département des manuscrits, Latin 9428 f.91)
S. Arnould, évêque de Metz (St. Arnulf, Bishop of Metz), July 18th, 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

Lives of the Saints by Alban Butler.

Lives of the Saints by Sabine Baring-Gould.

Medieval Hagiography

BHL, Supplement 

Acta Sanctorum

The Golden Legend

Art & Architecture

Index of Medieval Art

Portail Biblissima

POP : la plateforme ouverte du patrimoine

Europeana

Warburg Institute Iconographic Database 

Saints and their Attributes

The Saints in Art by Joseph Maria von Radowitz.

Emblems of Saints by Which They Are Distinguished in Works of Art by F. C. Husenbeth.

Music

Cantus: A Database for Latin Ecclesiastical Chant

Customs & Devotions

Late Medieval French Prayers