London Bridge. London Bridge is a historic bridge spanning the River Thames in London, connecting the City of London to Southwark. In art, London Bridge is often portrayed as a symbol of London’s history and transformation, depicted in various styles from medieval representations of its fortified structure and bustling markets to more modern interpretations emphasizing its connection to the city's urban development. It appears in paintings, engravings, and photographs, sometimes symbolizing change, such as in J.M.W. Turner's atmospheric landscapes, and in more contemporary works, where it can evoke themes of industrialization or nostalgia for the city's past. Several bridges named London Bridge have spanned the River Thames between the City of London and Southwark, in central London. The current crossing, which opened to traffic in 1973, is a box girder bridge built from concrete and steel. It replaced a 19th-century stone-arched bridge, which in turn superseded a 600-year-old stone-built medieval structure. This was preceded by a succession of timber bridges, the first of which was built by the Roman founders of London. The current bridge stands at the western end of the Pool of London and is positioned 30 metres upstream from previous alignments. The approaches to the medieval bridge were marked by the church of St Magnus-the-Martyr on the northern bank and by Southwark Cathedral on the southern shore. Until Putney Bridge opened in 1729, London Bridge was the only road-crossing of the Thames downstream of Kingston upon Thames. London Bridge has been depicted in its several forms, in art, literature, and songs, including the nursery rhyme London Bridge Is Falling Down. The modern bridge is owned and maintained by Bridge House Estates, an independent charity of medieval origin overseen by the City of London Corporation. It carries the A3 road, which is maintained by the Greater London Authority. The crossing also delineates an area along the southern bank of the River Thames, between London Bridge and Tower Bridge, that has been designated as a business improvement district. The abutments of modern London Bridge rest several metres above natural embankments of gravel, sand and clay. From the late Neolithic era the southern embankment formed a natural causeway above the surrounding swamp and marsh of the river's estuary; the northern ascended to higher ground at the present site of Cornhill. Between the embankments, the River Thames could have been crossed by ford when the tide was low, or ferry when it was high. Both embankments, particularly the northern, would have offered stable beachheads for boat traffic up and downstream-the Thames and its estuary were a major inland and Continental trade route from at least the 9th century BC.