Old London Bridge, 1207-1832
Old London Bridge was the first, and until 1750, the only bridge to cross the River Thames in London, England. There had been wooden bridges there since Roman times, but being very vulnerable to fire and to attack it was decided that a stone bridge should be built.
Building of the stone bridge began in 1176 and took 30 years to complete. The bridge was an amazing structure, 926 feet wide, spanning the river in 20 arches, one of which included a drawbridge which could be raised to allow tall ships through. The piers supporting the arches were 20 feet across, resulting in a significant reduction of the actual width where the water could flow, causing the river to really race through when the tide was flowing. At each end of the bridge Gate Houses protected the population from attack from the north or south.
The bridge was quite a good place to set up home in those days, with a constant supply of running water at hand and no problems with the latrines (hopefully any 'solid matter' fell directly into the river and not on any hapless passer-by). Thousands of people lived on the bridge and by 1358 there were as many as 138 large houses and shops, some of them 7 storeys high, and also a chapel dedicated to St. Thomas Becket - this resulted in the throughway being reduced to a mere 12 feet in width.
Over the centuries the population was ravaged by many fires and episodes of the plague. At one point in 1282, ice caused the collapse of 5 of the arches. Despite this, everything was always quickly rebuilt and people continued to live here until the houses were removed in 1762 to widen the road to 46 feet. At this time the two central arches were made into one large span by removing the central pier. This was the bridge's undoing, for water erosion then undermined the rest of the structure and it became impossible to maintain. A New London Bridge was ordered a few yards upstream.
New London Bridge, 1831 - 1971; 1971 -
The new bridge was designed by John Rennie and comprised 5 arches with a span of 150 feet in the middle, 140 feet next to that, and 130 feet on the outer arches. John Rennie died before work was begun, so the bridge was built by his 2 sons, and took 7 years to complete. A year after opening the new bridge, the old one was demolished.
The length of service of the New London Bridge was to be nothing like that of the old one. Less that 140 years after completion it could no longer cope with the huge increase in traffic across it and started to crumble. Maintenance became an impossible task and the bridge was put up for sale. The winning bid was made by Robert McCulloch, Founder of Lake Havasu City, Arizona, and London Bridge was sold for $2,460,000.
Slowly and painstakingly each stone was carefully numbered and removed, shipped to California and then taken by truck to Arizona. Reconstruction began on September 23, 1968, with a ceremony where the Lord Mayor of London laid the first cornerstone. On October 10, 1971, the bridge was dedicated and now stands as a tourist attraction on Lake Havasu on the Colorado River.
Modern London Bridge, 1972 -
In 1968 contruction began on a new bridge using beams of
prestressed concrete spread out from two piers. The bridge uses the
cantilever method to hold the beams in place, and was a very innovative design when it was first built.
http://www.saradouglass.com/bridge.html
http://www.bbc.co.uk/history/3d/bridge.shtml
Encyclopoedia Britannica