Dr. John Rao describes the maturation of the idea of Crusading. This process of maturation is shown to have taken hundreds of years, from the 600's through the 1000's. Maturation involved the Heraclian "Crusade" versus the Zoroastrian Persian invaders of the Eastern part of the Empire in the early Seventh Century. Icons were symbols used in crusading at this time. Taken from: Crusading, the Crusader & the Christian Order - 2002 VonHildebrand Institute