The interwar period (1918–1939) was a time of major development in the city's infrastructure. New modernist housing estates were built in Mokotów to de-clutter the densely populated inner suburbs. In 1921, Warsaw's total area was estimated at only 124.7km2 with 1 million inhabitants–over 8,000 people/km2 made Warsaw more densely populated than contemporary London. The Średnicowy Bridge was constructed for railway (1921–1931), connecting both parts of the city across the Vistula. Warszawa Główna railway station (1932–1939) was not completed due to the outbreak of the Second World War.