“Built to reduce pedestrian traffic jams, its construction in the ‘seventies was considered as a miracle of engineering.”
The 1870s, of course.
The Tower Pedestrian Subway under the Thames, built by Peter W. Barlow and James Henry Greathead took only about a year to complete. This wasn’t the first subway tunnel, that was the Thames Tunnel at Wapping completed in 1843 meant for the future London Underground. However, it was only the second due to problems encountered by that tunnel’s creator, Marc Brunel. Yet at 34, Greathead “tendered for the construction of the shafts and tunnel for £9400, devising a cylindrical wrought iron shield forced forward by 6 powerful screws as the material was excavated in front of it.”
According to Nicholas Bentley in The Victorian Scene: 1837-1901, “it runs a quarter of a mile beneath the Thames between Tower Hill and Bermondsley.”
(Go here to view pictures of the tunnel: http://www.victorianweb.org/technology/engineers/tunnel1.html)