The ancient Roman basilica and forum was once the largest building of its kind north of the Alps

Deep beneath the heart of the City of London lies a secret that most commuters walk over without a clue. It's the site of a vast Roman basilica and forum - a complex so large it once dwarfed St Paul's Cathedral.

Built around AD 70, this wasn't just any building. The basilica served as the civic and administrative hub of Londinium, the Roman settlement that would eventually become modern London. Inside, there was a civic centre, law courts, a treasury, and a marketplace all rolled into one. It was the beating heart of Roman London, a place for politics, trade, and gossip.

Covering nearly two hectares of land and reaching up to three storeys high, the basilica was a statement of Roman power and engineering. At its peak, it was the largest structure of its kind anywhere north of the Alps.

Beside it stood a grand open-air forum, the Roman equivalent of Trafalgar Square. This was where merchants sold goods and citizens gathered for announcements.

But the story of London's Roman forum didn't end well. By around AD 300, the city had backed a rebel emperor named Carausius - and Rome retaliated by destroying the basilica and forum in punishment.

For more than 1,500 years, the remains of this once-mighty structure were lost. That is, until the 1880s, when builders working on Leadenhall Market accidentally uncovered fragments of the basilica's arches.

Those first discoveries lay hidden beneath what used to be a barber's shop at the corner of Gracechurch Street and Leadenhall Market. The remains are still in the site's basement, but unfortunately, the shop has closed down.

Then, in 1987, construction workers made another astonishing find at 21 Lime Street. Archaeologists from the Museum of London uncovered floors and walls dating back to the Boudican fire of AD 60 - the earliest evidence of Roman rebuilding after the revolt.

Excavations in the 1990s and early 2000s revealed even more of the site's east wing, including flooring from the original forum.

Today, the site at 21 Lime Street is fenced off. But if you know where to look, you can still glimpse the ground where archaeologists unearthed London's Roman past.

This is a striking reminder that the modern City of London, with its glass towers and trading floors, was built on a place of power nearly two millennia ago.

From Roman law courts to financial giants, the heart of London has always been a centre of influence. You just have to dig a little deeper to find where it all began.