The crisis provoked by the spread of heresy led to a major change in the religious life of Christendom, a change that occurred initially in southern urban Europe where the Cathars and Waldensians also found their strongest support. To put the matter simply, Catholicism found its own wandering poverty preachers. The friars, from the Latin fratres, for 'brothers', were religiously orthodox. Francis of Assisi had many points in common with Valdes. He was inspired in his twenties by the ideal of the apostolic life. Sometimes modern scholars describe the friars as just another variety of monk, but in fact they intended to be something very different. The Spiritual Franciscans inspired and associated with other groups who practised radical poverty, like the Apostolic Brethren and the Dolcinites. Some of the greatest thinkers of the Middle Ages were Dominicans, including Albertus Magnus and Thomas Aquinas.