View of Heidelberg, Germany, including the Neckar River and the Holy Ghost Church. The medieval church was built between 1398 and 1441 on a site where a Roman basilica once stood. It once housed the worldâ€™s largest library; but in 1622, during the Thirty Years War, the books were seized by General Tilly and the army of the Holy Roman Empire and sent to the Vatican. For 230 years â€“ between 1706 and 1936 â€“ the church was used by both Lutherans and Catholics, with a wall down the center separating the congregations. Today, it is a Protestant church.