Workers renovate the Crossrail Connaught tunnel between the Royal Albert and Royal Victoria docks in east London, on May 29, 2013.
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When one digs beneath London, England, one digs through history. Crossrail, the largest construction project in Europe, is tunneling under the British capital to provide a new underground rail link across the city, and has encountered not only a maze of existing modern infrastructure, but historic finds including mammoth bone fragments, Roman roads (with ancient horseshoes embedded in the ruts), Black Plague burial grounds, and 16th century jewelry. The $25 billion (15 billion pound) project is due to open in 2018, connecting London's Heathrow airport to the county of Essex -- five tunnel boring machines are creating a kilometer of new tunnel under London every two weeks. The millions of tons of soil from the Crossrail construction are being shipped to Wallasea Island in the Thames Estuary, allowing the island to be transformed from levee-protected farmland into a thriving wetland.