During the 17th century, the Hall of Mirrors was used by Louis XIV when he walked from his private apartment to the chapel. At this time, courtiers assembled to watch the king and members of the royal family pass. In 1745 the Hall was the scene of "The Yew Tree Ball". It was at this event that Louis XV met Madame de Pompadour. In the 19th century, the Prussian king, William I, was declared German emperor on 18 January 1871 in the Hall of Mirrors by Bismarck and the victorious German princes and lords. French Prime Minister Clemenceau chose the Hall of Mirrors to sign the Treaty of Versailles that ended World War I on 28 June 1919. The Hall of Mirrors still serves for state occasions such as receptions for visiting heads of state.