The site was discovered at 85 Gracechurch Street, an office building that’s about to be demolished and redeveloped.
Earlier archaeological investigations revealed the ancient basilica’s approximate location, so the team created several small test pits to see what was hidden beneath the concrete floor.
On the third attempt, digging between the filing cabinets, they struck lucky.
“You can see a huge chunk of Roman masonry, and it’s incredible that it survives this well. We’re absolutely thrilled that there’s so much of it here,” said Sophie Jackson.