It has become fashionable in British archaeological circles to criticize airphotographers for continuing to reconnoitre the better-known districts such as the upper Thames valley or the Yorkshire Wolds, when they might be using their limited flying time to explore areas where little or nothing has yet been recorded from the air. The importance of making flights over the less rewarding ground is undeniable, but it is quite wrong to assume that the ‘classic’ crop-mark areas have nothing more to reveal. Every year brings major aerial discoveries on the chalklands and river-gravels of southern Britain, and their value is enhanced – not diminished – by the body of knowledge already available for each locality. Individual sites, although revisited year after year, may display vital new information only after literally decades of scrutiny, and continued surveillance is called for if air-photography is to play a fully effective part in archaeological exploration.