When was the earliest observed #CropMark recorded #mastadon? I have C.16th British antiquary John Leyland in pole position (tailend?) with reference to local folk describing the 'St Augustine's crosses' -thought to be buried cross roads within the Romano British town of Silchester- observed in CE 1541... Long before #AerialArchaeology and #RemoteSensing ... I haven't tracked them down yet but I expect much earlier observations, eg in classical writings? Saturday #ShadowSites