The document summarizes the rise and spread of Christianity from the fall of the Roman Empire to the Late Middle Ages. During this period, Christianity grew from a small persecuted sect to the dominant religion of Europe. It established a church hierarchy with the Pope at its head and adopted core beliefs and sacraments. The Crusades were a series of military expeditions called by the Pope in the 11th-13th centuries to recover the Holy Land from Muslim rule, though they ultimately failed in their goal.