ROMAN STONES

In the Vatican's Museo Pio-Clementino are dozens of galleries crammed with the treasures of Imperial Rome. Among them are these urns carved from wonderful stones: onyx, agate, chalcedony. There's something extraordinary about the simple, classical shapes with the bold, bizarre markings of the stones, which give them such depth and life. They capture perfectly the crazy luxury of the period, even as presented in the austere, neutral setting of the 1771 museum rather than the wild kitsch that once surrounded them.

The enormous bowl of porphyry above - the largest piece ever found, 4.5m diameter - from the Baths of Titus, given by Ascanio Colonna to new Pope Julius III for his Villa Giulia in 1550, went after his death to the Vatican's Belvedere Court for 200 years, and then to the Museo Pio-Clementino where it remains, with the (supposed) sarcophagus of St Helena, above right. Below: Dacian captives with porphyry clothes from Trajan's Forum, in the Boboli gardens, Florence, and a Gaul robed in camouflage-style marble in the Louvre; the legs of a striding, Ptolemaic Egyptian and another huge bowl, this one in yellow onyx with a bearded god, in the Louvre again. The size, the simplicity, the boldness of the gesture: all astonish.