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19 November 2013 Last updated at 14:24 GMT
Engineers have used a tunnelling machine called Phyllis to dig through 6.8km (4.2m) of earth from Royal Oak in west London to Farringdon on the edge of the City.
BBC London's Chris Rogers took a look around the tunnel and spoke to the project manager of Western Tunnels, Andrew Alder.
Crossrail has completed its first train tunnel 18 months after work began.