The Cathedral of the Protection of Most Holy Theotokos on the Moat, popularly known as Saint Basil's Cathedral, is a Russian Orthodox cathedral erected on the Red Square in Moscow in 1555–1561. Built on the order of Ivan IV of Russia to commemorate the capture of Kazan and Astrakhan, it marks the geometric center of the city and the hub of its growth since the 14th century. It was the tallest building in Moscow until the completion of the Ivan the Great Bell Tower in 1600.