For centuries, the London Bridge was one of the world's most important bridges — until the Westminster Bridge opened in 1750, it was the only structure to reach across London's River Thames. John Rennie and his son designed and constructed the most famous of the London Bridges, which opened in 1831. When it was discovered that one end of the span was sinking, it was decided to sell the bridge. Robert P. McCulloch bought the landmark for some $2.5 million, dismantled it and moved it to Arizona, where it was re-erected and opened on this date in 1971. The London Bridge now spans a canal in Lake Havasu City.