The Church's power

In medieval Europe, the Catholic Church was not just a religious institution -- it was arguably the most powerful organization on the continent. It collected a tithe (about one-tenth of income) from nearly everyone, ran its own courts under canon law, and could excommunicate (formally expel) even a king, which many people at the time believed put that person's soul in danger. Monasteries, meanwhile, were centers of learning in an age when few people outside the clergy could read -- monks spent years hand-copying manuscripts, including ancient Roman and Greek texts, preserving them for future centuries much as scholars did in Baghdad and Cordoba.

The Church's power sometimes rivaled or exceeded that of kings, and the Investiture Controversy shows exactly how far that could go. Pope Gregory VII and the Holy Roman Emperor Henry IV clashed in the 1070s over who had the right to appoint bishops -- the pope, or the emperor. When Gregory excommunicated him, Henry, in 1077, famously stood outside the pope's residence at Canossa for three days in the snow, seeking forgiveness -- a striking image of a king humbling himself before religious authority, even though the underlying political struggle over power continued for decades afterward.