There has been no space for new buildings in Central London many years now. In fact, this was a problem that city planners had to deal with as long ago as the 19th . They decided the only way to expand was to go down. So they dug. Railways, roads, footpaths, sewers - they even buried rivers underneath the streets of London. Recent construction work in the heart of London uncovered even more of London's underground past. Workers found a hidden world from Roman times.

In one recent development, construction workers unearthed the old High Street of Roman London, follows exactly the line of today's main roads through the City of London.

There are even secrets under the River Thames which has around 30 tunnels beneath it. The first of these built by Marc Brunel back in the 1800s. He began work in 1825 - it was a very difficult job and it him and his men 15 years to finish. But the tunnel finally opened in 1840 and was a great success. Some years it was closed to the public and used for a railway line.

of the biggest underground networks in London is, of , the underground railway , also known the Tube. Some Tube lines are a more than hundred years old and several recently closed. For example, the tiny line to Aldwych, the heart of London's theatre district, was closed in the 1990s. The empty station is now hired out for films and parties. Aldwhich is one of 40 ghost stations thoughout the city. Another is a station called British Museum, which some people say was closed an Egyptian mummy had escaped from the nearby museum and was haunting the station !