 After Maidan Castle , Wheeler turned his attention to France , where the archaeological investigation of Iron Age sites had <unk> behind developments in Britain . There , he oversaw a series of surveys and excavations with the aid of Leslie Scott , beginning with a survey tour of Brittany in the winter of 1936 – 37 . After this , Wheeler decided to excavate the oppidum at Camp d <unk> , near <unk> , <unk> . In addition to bringing many British archaeologists to work on the site , he hired six local Breton <unk> to assist the project , coming to the belief that the oppidum had been erected by local Iron Age tribes to defend themselves from the Roman invasion led by Julius Caesar . Meanwhile , Scott had been placed in charge of an excavation at the smaller nearby hill fort of <unk> , near <unk> . In July 1939 , the project focused its attention on Normandy , with excavations beginning at the Iron Age hill forts of Camp de Canada and <unk> . They were brought to an abrupt halt in September 1939 as the Second World War broke out in Europe , and the team evacuated back to Britain . Wheeler 's excavation report , co @-@ written with Katherine Richardson , was eventually published as Hill @-@ forts of Northern France in 1957 . 
