A flock of grazing sheep is helping archaeologists to preserve the ancient ruins of Pompeii, the Roman city that was buried under metres of pumice and ash in the calamitous eruption of Mount Vesuvius in AD 79.

Archaeologists have uncovered only around two thirds of the 66-hectare (163 acres) site at Pompeii since excavations began 250 years ago. Preserving the unexplored sections of the ancient city against erosion by nature and time is a priority for those who manage the site.