Detail from Harleian ms. 3244, folios 27-28, showing an allegorical knight preparing to battle the seven deadly sins with the "Scutum Fidei" diagram of the Trinity as his shield.

This is part of a ca. 1255-1265 illustration to the Summa Vitiorum or "Treatise on the Vices" by William Peraldus.

An overview of the whole illustration is available at File:Peraldus Vices and Virtues.jpg, and the depiction of the knight is at File:Peraldus Knight.jpg.

For detailed discussion of the manuscript, see the article "An Illustrated Fragment of Peraldus's Summa of Vice: Harleian MS 3244" by Michael Evans in Journal of the Warburg and Courtauld Institutes, vol. 45 (1982), pp. 14-68.

The Latin text on the shield in the image includes monograms and/or scribal abbreviations for "PATER" (the Father), "SPIRITUS" (the Holy Spirit), and "FILIUS" (the Son) in the three outer nodes, and "DEUS" (God) in the center node. The text in the links connecting the outer nodes to each other reads "Non est • nec e converso" (i.e. "Is not, and vice versa", indicating that a link connecting two outer nodes A and B encodes both of the propositions "A is not B" and "B is not A"). The text along the links connecting the center node to the outer nodes is quite obscured, but according to Evans should read "Est et e converso" (i.e. "Is, and vice versa", indicating that both "God is A" and "A is God" for each of the three persons of the Trinity).

For the history and meaning of this general "Shield of the Trinity" or "Scutum Fidei" diagram of traditional western Christian symbolism (a visual summary of the first part of the Athanasian Creed), see the main article en:Shield of the Trinity. For other versions of the diagram on Wikimedia Commons, see Image:Wernigeroder_Wappenbuch_010.jpg,