The Romans were the first to construct a bridge crossing the River Thames during the 1st century. Two former spans were called the London Bridge. The medieval version was constructed in 1209. The second was finished in 1831. When it came time for a replacement, it was sold to Robert McCulloch in 1968 and reassembled in Arizona. The iconic Tower Bridge was constructed downstream in 1894. The length is 801 feet and the twin towers are 213 feet tall. Two center bascules can be raised in five minutes to allow the passage of tall ships. In the elevated walkway and beneath the facade of Portland stone and Cornish granite are 11,000 tons of steel.