In 1939, King George VI and Queen Elizabeth, on a visit to Niagara Falls, dedicated the site for the construction of the Rainbow Bridge. The site is marked with a monument on the Canadian shore commemorating the occasion and construction began on May 4th, 1940. The bridge officially opened on November 1st, 1941. The Rainbow Bridge, which spans the Niagara River Gorge just a few hundred meters below the falls, is the main border crossing between Niagara Falls, New York and Niagara Falls, Ontario. With a spam of 289.5 metres (950 feet), it is estimated that 2.75 billion kilograms (over 6 billion pounds) of water cross under the Rainbow Bridge every minute.