'Hidden treasure' Mystery remains after discovery of vaults under new museum

When a contractor working on the site of the new London Museum at Smithfield market knocked a tentative hole in a bricked-up basement wall, all he could see, peering in with a torch, was a muddy pile of rubble and some scurrying rats.

- Esther Addley

But behind the wall, once the detritus had been carefully removed, the architects and builders were astonished to find an enormous and beautifully constructed network of brick vaults that no one, even a year into the ambitious £150m project, had known were there.

There had been hints on old plans of some underground structures, "but because everything was blocked in and bricked up, we had no idea that they still existed", said Paul Williams, principal director of the lead architects, Stanton Williams.

Certainly nothing had suggested the sheer scale of the surviving Victorian vaults, a labyrinthine forest of carefully hand-built arches and columns which stretch to 800 sq metres (8,600 sq ft), an area bigger than three tennis courts - all hiding in one of the busiest parts of central London.

If breaking through the wall was "a little bit Indiana Jones", the discovery itself was "magical", said Williams. He was enchanted by the project to convert two historic former food markets at Smithfield, near Farringdon, into a new home for the Museum of London after the closure in 2022 of its previous home at the Barbican.