Sir Christopher Wren was 33 years old and near the beginning of his career as an architect when the Great Fire of London in 1666 destroyed many of the city's public buildings, including 88 of its parish churches. Wren's office was commissioned to build 51 replacement churches and St Paul's Cathedral. Many of these buildings survive to this day; others have been substantially altered or rebuilt. Some others were completely or partially destroyed during the German Blitz of 1940–41; yet others were demolished for different reasons.