THE presence of ‘crop marks’ in aerial photographs is frequently used to detect archaeological features. These marks are produced by differences in plant size or colour which are related to the characteristics of the soil overlying or comprising the man-made feature. Pure stands of many arable crop species are known to show visible responses to soil heterogeneity. In the case of woody perennials we have found only one report describing the detection of archaeological structures by virtue of their influence on the growth of a crop1. This was the identification of ancient hut sites in Kenyan tea plantations where excess lime caused failure of the crop. We now report the detection of an ancient field system by virtue of its present-day relationship to patterns of a disorder in beech (Fagus sylvatica L.).