The plan was to demolish the old office building at 85 Gracechurch Street in the heart of London’s financial district and construct a new 32-story tower in its place. But as demolition began, archaeologists made a staggering discovery in the site’s foundation: remarkably intact ruins of London’s first public building,

Archaeologists exploring the site of a planned 32-story office tower announced Thursday that they have unearthed the remains of a Roman basilica that once stood at the heart of the city known as Londinium.

An office building from the 1930s in London was about to be demolished — until remnants of the city’s first Roman basilica were found in the basement.