Harry Potter's Leadenhall Market Sits on Roman London's Giant Basilica

In the first Harry Potter film, Hagrid leads Harry through a glass-roofed Victorian market to the door of the Leaky Cauldron. That market is Leadenhall Market in the City of London, and the ground beneath it hides a far older giant. Around AD 120, this exact spot held the basilica of Roman Londinium, a hall roughly 150 meters long that was the largest Roman building of its kind north of the Alps.

A basilica, in Roman terms, was not a church. It was the civic heart of a town: a covered hall where courts sat, officials kept their offices and the local council met. It stood on one side of the forum, an open square lined with shops where Londoners traded and gathered.

London actually had two of them. The first forum and basilica went up in the late 70s or 80s AD, probably under the governor Agricola, on the high ground east of the Walbrook stream. According to the Museum of London, that first complex measured about 100 by 50 meters. Within a few decades the city had outgrown it.

Work on a replacement began around AD 100 and took roughly 30 years. Builders raised the new walls around the old complex, which stayed open for business, and only demolished the first basilica once its successor was nearly done. The new forum covered a square of about 167 meters per side, and its basilica rose three storeys high. The magazine Current Archaeology notes it was bigger than today's St Paul's Cathedral and sat beside a forum about the size of Trafalgar Square.

The eastern part of that basilica lies under Leadenhall Market. When architect Horace Jones rebuilt the market in 1881, workers hit the base of one of the basilica's arches. For years, visitors could ask to see a surviving pier base, preserved behind glass in the basement of a hairdresser at 90 Gracechurch Street, at the market's edge.

Even the first, smaller basilica turned out to be in better shape than anyone expected. In early 2025, MOLA archaeologists digging in the basement of 85 Gracechurch Street, next to the market, uncovered massive foundations of flint, ragstone and Roman tile, some more than 10 meters long, 1 meter wide and 4 meters deep. Historic England said they probably belong to the tribunal, the raised platform where magistrates gave judgments. The owners plan to display the remains in a public space expected to open around 2029 or 2030.

The market above has its own long history. A market has operated here since the 14th century, and the current ornate roof of green, maroon and cream ironwork is the 1881 design by Jones, who also built Smithfield and Billingsgate markets. The building has been Grade II* listed since 1972.

Its film career came almost by accident. Director Chris Columbus was searching for a Leaky Cauldron entrance when he came across an unrenovated optician's shop on Bull's Head Passage. Its owner told Time Out that the old, worn front door was perfect for a wizards' pub. For the third film, the Leaky Cauldron moved to Borough Market, but fans still visit the original door every day.

So the next time someone poses at that door for a photo, they are standing a few meters from where Roman judges once presided over Britain's largest city, almost 1,900 years before a boy wizard walked by.

Sources: Museum of London, Londinium Today: Basilica and forum; MOLA (2025); Historic England (2025); Current Archaeology (2025); Brigham, Britannia (1990); Historic England listing; Time Out London. Cover: Leadenhall Market interior by Diliff.