The Italian marble plaque likely was created between 50 and 150 AD and would have been placed prominently either on a building or in a shrine. It was found in the Southwark (near the former location of the Tabard Inn of Chaucer’s Canterbury Tales) area of London at the junction of three key Roman roads. It bears a dedication inscription to the Roman emperors and the god Mars from London-based merchant Tiberinius Celerianus, a name with Northern Gaulish antecedents. There’s an image of the plaque here, in this CNN article.