How did the sale of indulgences raise money for St. Peter’s Basilica under Leo X?

Under Pope Leo X, the sale of indulgences was utilized as a financial mechanism to fund the reconstruction of St. Peter’s Basilica in Rome. Because the papacy faced significant financial strain from various obligations—including war, support for the arts, and the basilica's construction—Leo X authorized the sale of a special plenary indulgence to generate necessary revenue.21

The process functioned through a system of commutation, where the temporal punishment for sin could be remitted in exchange for a monetary contribution. In Germany, Archbishop Albert of Mainz was granted permission by the pope to conduct this sale to help pay off debts he had incurred to secure high church offices. By secret agreement, half of the proceeds collected in Germany were diverted to the Fugger banking house to satisfy Albert’s creditors, while the remaining portion was intended for the basilica project. This practice, particularly the aggressive marketing by agents like Johann Tetzel, became a major source of scandal and a primary catalyst for the Reformation.234