Palmyra is in danger. As Islamic State fighters clash with Syrian government forces around the historic site, it is worth considering what the loss of this wonder, dubbed the "Venice of the Sands", would mean for the world's cultural heritage.

Palmyra is the last place anyone would expect to find a forest of stone columns and arches. Travellers in the 17th and 18th centuries were repeatedly astonished by what they saw: a vast field of ruins in the middle of the Syrian desert, roughly half-way between the Mediterranean coast and the valley of the River Euphrates.

For anyone visiting, however, the key reason for the site's prosperity is immediately apparent: ancient Palmyra sits at the edge of an oasis of date palms and gardens.