historic buildings. This policy, 'St Paul’s Heights', has officially been in operation since 1937. Concerns about aesthetics and fire safety had likewise hampered the development of skyscrapers across continental Europe for the first half of the 20th century. Some notable exceptions are the tall 1898 Witte Huis (White House) in Rotterdam; the tall PAST Building (1906-1908) in Warsaw, the Royal Liver Building in Liverpool, completed in 1911 and high; the tall 1924 Marx House in Düsseldorf, Germany; the Kungstornen (Kings' Towers) in Stockholm, Sweden, which were built 1924–25, the Edificio Telefónica in Madrid, Spain, built in 1929; the Boerentoren in Antwerp, Belgium, built in 1932; the Prudential Building in Warsaw, Poland, built in 1934; and the Torre Piacentini in Genoa, Italy, built in 1940. After an early competition between New York City and Chicago for the world's tallest building, New York took the lead by 1895 with the completion of the tall American Surety Building, leaving New York with the title of the world's tallest building for many years. Modern skyscrapers Modern skyscrapers are built with steel or reinforced concrete frameworks and curtain walls of glass or polished stone. They use mechanical equipment such as water pumps and elevators. Since the 1960s, according to the CTBUH, the skyscraper has been reoriented away from a symbol for North American corporate power to instead communicate a city or nation's place in the world. Skyscraper construction entered a three-decades-long era of stagnation in 1930 due to the Great Depression and then World War II. Shortly after the war ended, the Soviet Union began construction on a series of skyscrapers in Moscow. Seven, dubbed the "Seven Sisters", were built between 1947 and 1953; and one, the Main building of Moscow State University, was the tallest building in Europe for nearly four decades (1953–1990). Other skyscrapers in the style of Socialist Classicism were erected in East Germany (Frankfurter Tor), Poland (PKiN), Ukraine (Hotel Ukrayina), Latvia (Academy of Sciences), and other Eastern Bloc countries. Western European countries also began to permit taller skyscrapers during the years immediately following World War II. Early examples include Edificio España (Spain) and Torre Breda (Italy). From the 1930s onward, skyscrapers began to appear in various cities in East and Southeast Asia as well as in Latin America. Finally, they also began to be constructed in cities in Africa, the Middle East, South Asia, and Oceania from the late 1950s. Skyscraper