1/2. In a cliff near Dunhuang on the Silk Road in north-west China, there are hundreds of caves cut and painted by Buddhist believers over a millennium. Early last century, thousands of scrolls, pictures and artefacts were taken from this great gallery in the desert and dispersed to museums and collections all over the world. Now they are being reunited on the internet. Isabel Hilton visits the caves, Beijing and the British Library and tells a story of international co-operation and digital technology that is leading to the creation of a virtual Dunhuang. Producer Julian May