The 2,000-year-old basilica was “once the beating heart of Roman London,” the Museum of London Archaeology said.

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.

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.