During the war and in the immediate post-war period the Royal Air Force and the United States Army Air Force undertook a considerable air survey programme covering Burma, Siam and French Indo-China. In Siam the initial cover was restricted to large-scale (1:15,000 and better) photographs of towns, airfields and communications. Later a more ambitious programme of survey cover (scales 1 : 50,000 and 1 : 25,000 with a few towns and beaches at larger scale) was undertaken, and practically the whole of the country has been covered by air photographs of one scale or another.

It has been my privilege to serve with the R.A.F. in Siam on both ground and flying duties and, more recently, to be in a position to examine most of the photographs taken. A very considerable number of archaeological sites have come to light, many being noted for the first time ; and it is my intention in this initial paper to comment briefly on one particular type of earthwork which appears to have a limited distribution in eastern Siam. The air photographs are reproduced with the sanction of the Air Ministry.

It must be emphasized that although Siam, the meeting place of Indian and Chinese cultures, is rich in archaeological sites very little systematic work has yet been undertaken. On the one side the natural reluctance of the Siamese to disturb ancient sites and, on the other, comparative absence of trained archaeological research workers have been contributory factors. Detailed ground information generally is lacking and it follows that these notes are based on air photographic evidence, in most cases without ground checking, an impropriety of which the writer is only too well aware.