The Pius and Clement Museum, which is part of the Vatican Museums, was founded in 1773, and is named after the two popes who oversaw its founding. The museum fills several large exhibition halls and contains many ancient Roman sculptures and artifacts. The Papal States were forced - following the Treaty of Tolentino in 1797 - to give up the main masterpieces in the Museum to Napoleon, and they were transferred to Paris; After the defeat of Napoleon and the convening of the Congress of Vienna (1815) and thanks to diplomatic efforts, a large part of these works were recovered.