I. Introduction.- II. The Arts and The Reform of the 11th Century.- III. The Textual and Typological Sources of the Cleansing.- IV. Two Historic Personalities:.- 1. Gregory VII.- 2. Countess Matilda.- V. Medieval Commentators on the Cleansing.- 1. Peter Damian.- 2. Humbert of Silva Candida.- 3. Anselm of Lucca.- 4. Bruno of Asti.- VI. The Patarines.- VII. Four Illuminations Related to the Cleansing:.- 1. The Matthew Portrait.- 2. The Arrest of Christ.- 3. The Third Temptation.- 4. The Baptist Preaching.- VIII. Conclusion.- Plates.