In 1562, workers in a vineyard near Rome unearthed ancient marble fragments - pieces of the Severan Marble Plan, a detailed map of Rome created in the third century AD. Since then, 1,186 pieces have been found, an unrivalled archaeological treasure, revealing the topographical and social structure of ancient Rome. Vanessa Collingridge travels to the Eternal City to recount the story of this unique map and how computer technology is helping to piece together an ancient Roman jigsaw puzzle.