• Innocent III, De summa trinitate, the full text from which Bartholomew quotes
• Richard of St. Victor on the Trinity
• Charles Hodge, Systematic Theology
• Catholic Encyclopedia
• Wikipedia

Art

• Illumination from De proprietatibus rerum by Bartholomew the Englishman
• Holy Trinity, Palace of the Legion of Honor, San Francisco,
  California
• Princeton University, Garrett MS 28, 243r
• Trinitarian iconography, National Library of the
  Netherlands

Trinitarian Symbolism

• The Origin of the Triquetra
• The Shield of the Trinity
• Number Symbolism in the Middle Ages (Paul Calter, 1998,
  Dartmouth College)

• Islamic Web
• Jewish Encyclopedia
• Hindu Website