Archaeologists have found a substantial piece of the ancient city’s first basilica - a 2,000-year-old public building where major political, economic and administrative decisions were made.

The excavation has so far revealed sections of stone wall that formed the base of the basilica, which would have been two-and-a-half storeys high.

The site, which will eventually be opened to the public, sheds light on the city’s beginnings.

“This is so significant - this is the heart of Roman London,” said Sophie Jackson, from the Museum of London Archaeology (Mola), who revealed the new find exclusively to BBC News.

“This building will tell us so much about the origins of London, why London grew and why it was chosen as the capital of Britain. It’s just amazing.”

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.