If your enjoyment of this article is impaired by a sickening splintering noise, it'll be TV's Tony Robinson gnashing his teeth. In the competitive world of popular archaeology, the New Statesman has pulled the duckboards out from under the host of Time Team. Let me draw your - and his - attention to the accompanying photo. The viewing public's favourite foil to history isn't the man I think he is if he fails to recognise Britain's brand-new ancient attraction. As Robinson is informing his cowering researchers at this very moment, it's nothing less than London's Roman amphitheatre underneath the Guildhall Art Gallery. (It's there, by the way, for the very good reason that that's where they found it, when they finally got around to making good some Blitz damage in 1988.)

The arena may eventually get the distinctive treatment of Robinson's Channel 4 programme, but I had the privilege of seeing it when it was still under reconstruction. My guide was Hedley Swain, who is in charge of early history at the Museum of London. Which is as well, since it would be a shame to waste a name like his. If you imagined someone cutting a dash at an excavation, with trowel and air-puffer and leather-patched sports jacket, you'd be hard put to think of a better name for him than Hedley Swain.

Hedley and I peeked under builders' tarpaulins to view the amphitheatre's substantial walls of ragstone and tile. They were introduced to prevent wild beasts from vaulting out of the ring and into the laps of startled spectators. A works manager called John was grappling with a problem that had confronted the original impresarios: what kind of flooring to go for? The Roman solution had been a bedding of gravel and mortar, dusted with soft sand. The hard layers afforded purchase to sandal and hoof alike, while the sand soaked up the blood. John's worry wasn't horseshoes and chariot wheels, but the impact of the millions of heels expected to traverse the battleground. The stadium once held as many as 6,000 fight fans, but Ridley Scott's Gladiator has excited a new generation with the thrills and carmine spills of the Roman games. Musing aloud about one surfacing option, John summed up its virtues with: "All the joy of pea-beach gravel, but without it being kicked around."

At the southern entrance to the site, researchers found a skeleton, prompting the museum's project leader Nick Bateman to ask: "Could this have been someone killed in London's amphitheatre?" But the museum has no need to embellish the passing of a bony local in order to tickle up trade. It can claim a genuine celebrity with links to the blood sports circuit of Roman London, in the beguiling form of a female gladiator. Strictly speaking, the form she's in is powder: she was cremated in Southwark. But votary offerings suggest that her funeral was conducted with full warrior honours. The lavender gladiator remains an unknown soldier of fortune. Inexplicably, she's failed to attract the nickname Glad.