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Location: London, England
Completion Date: 1863 (first line)
Length: 19,800 feet (3.75 miles)
Setting: Soft ground
Materials: Cast iron, brick
Engineer(s): Sir John Fowler
Shortly after the opening of the Thames Tunnel, Parliament authorized construction of the first subway system in the world, the London Underground. Work began in 1860 on the first stretch of the underground subway, the Metropolitan Railway. By all accounts, it was a royal mess. Tunnel diggers used the cut and cover method: they carved huge trenches in the streets, lined the trenches with brick, covered the trenches with arch roofs, and then restored the street above. This sloppy method paralyzed traffic and made canyons out of city avenues, but it was a huge success. The new subway carried more than nine million people in its first year!
Soon, Londoners were craving more, and they got it. This time, with the help of James Henry Greathead's tunnel shield, London engineers could tunnel under the city without completely destroying the streets above. Greathead's round iron shield supported the soft soil as it moved forward and carved a perfectly round hole hundreds of feet below London's bustling city streets. Inside the shield, tunnel workers laid cast-iron segments end to end. These segments eventually formed a stiff, waterproof tube, perfect for subways. Following London's lead, New York, Boston, Budapest, and Paris soon boasted subways of their own.Here's how this tunnel stacks up against some of the longest tunnels in the world.
(total length, in feet)