the eighth—ninth century A. D. But remains far older and of distinct artistic interest were revealed by the clearing of certain Buddhist shrines (Chapter XIII). The fine wall-paintings which adorned them, in places inscribed with Kharosthi legends, offered striking testimony to the powerful influence which Hellenistic art, as_transplanted from the Near East to Gandhara, had exercised even on the very confines of China.
Crossing in February—March, 1907, the Lop desert north-eastwards by the lonely track which Marco Polo, like early Chinese pilgrims before him, had followed, I was able to collect observations of interest both for the physical geography of the ground which separates the present terminal basins of the Tarim and the Su-lo Ho, and for the historical topography of the earliest Chinese route into Central Asia (Chapter xiv). Before reaching my new base at Tun-huang, I found myself rewarded by the discovery of the long-forgotten westernmost portion of that ancient frontier wall, a true Limes, which the Han emperor Wu-ti had constructed towards the end of the second century R. c. in order to guard his newly opened line for China's commercial and political expansion towards Central Asia against the raids of the Huns.
In Chapters XV—xIX I have described the explorations extending over two months and a half which enabled me to trace the line of the ancient wall, found often in remarkable preservation, for a total length of over 140 miles and to search the ruins of all its watch-towers and stations, including the famous ` Jade Gate '. Having remained undisturbed by the hand of man in the solitude of the gravel desert, they yielded a rich harvest of early Chinese and other records, mainly on wood, together with many interesting relics of the life led along this most desolate of borders during the centuries immediately preceding and following the time of Christ. Since the unsurpassed learning and critical acumen of M. Chavannes has rendered the great mass of the Chinese documents recovered here accessible to research,' it has become possible for me to discuss in Chapter xX the general organization of the Limes in the light of the historical and antiquarian information furnished by them, and thus to bring into correct focus the significance of the antiquarian facts revealed by actual exploration of the Limes.
But that region of Tun-huang had reserved for me another discovery very different in character but quite as fascinating and important. To the south-east of its main oasis, at the foot of a barren dune-covered hill chain, there lies the sacred site of Chien fo-tung, or the ` Caves of the Thousand Buddhas '. Buddhist piety from about the fourth century A. D. onwards has here honey-combed the rock walls of a true Thebais with hundreds of cave-shrines, still objects of worship (Chapter xxI). Their rich decoration with frescoes and stucco sculptures, much of it fine work of Tang times (Chap. xxv, sec. i), would alone have justified an archaeological pilgrimage from the Far West. Here I had the good fortune in May, 1907, to be the first European to gain access to a great deposit of ancient manuscripts and art relics of many kinds which had lain hidden and well-protected in a walled-up rock chapel for close on nine hundred years. The story how I secured here twenty-four cases of ancient manuscripts, most of them Chinese, but many also in Sanskrit, Khotanese, Kuchean, Sogdian, Manichaean and ' Runic ' Turkish, Uigur, and Tibetan, and five more cases filled with paintings, embroideries, fine textiles, and other artistic offerings of Buddhist devotion has been fully told in Chapter XXII.
The hundreds of fine paintings on silk here recovered may be said to have opened a new chapter in the history of Buddhist pictorial art as developed in Central Asia and China, largely under influences transmitted from Gandhara, and their study, inaugurated in Appendix E by such competent collaborators as the late M. Petrucci and AIr. L. Binyon, will need prolonged efforts. In Chapter xXiII I have not been able to attempt more than a systematic grouping of all pictorial relics
a See Chavannes, Les Documents chinois découverts par Aurel Stein, Oxford University Press, 1913, pp. 1-154.