Simon de Montfort (1165 – 1218), commander in chief of the French Crusades, was a friend and supporter of Dominic. Dominic first met this chivalrous knight is 1209 or shortly thereafter, and the two men became close friends. Both were engaged in combating heresy but in different ways: de Montfort by wielding the sword of battle, Dominic by wielding the word of God. An exemplary Christian soldier, de Montfort finally defeated Raymond, count of Toulouse, at the battle of Muret on September 13, 1213. To such an extent did de Montfort attribute his success to Dominic’s prayers that he erected a chapel dedicated to Our Lady of the Rosary in the church of St. James at Muret.
Dominic baptized one of de Montfort’s daughters, who subsequently became a Cistercian nun, and solemnized the wedding of his son Alembic. Another daughter, Aicia de Joigny, persuaded her son to join the Dominican Order, and she herself founded a monastery of Dominican nuns at Montargis, of which she became prioress. His younger son was an English soldier and statesmen. Simon de Montfort was killed during the siege of Toulouse in 1218.
The above excerpt is from Reflections of Dominican Spirituality: The Windows of St. Dominic Church, Washington, D.C. by Dr. Mary Moran.