Excerpts from Books and Wikipedia
"Under a series of intelligent and able abbots, Cluny spearheaded a movement for monastic reform that came to play a large part in the revitalization of the Church and papacy. . . . Wealth flowed to Cluny, and three abbey churches were built in quick succession; the last, begun in 1088, was the largest church in the world until St. Peter's in Rome was completed in the sixteenth century. . . . Four Cluniac monks became popes: St. Gregory VII, Urban II, Pascal II, and Urban V." [Furtado: 1001 Days]