Archaeologists use aerial photographs to spot archaeological sites from above. They show archaeological sites as cropmarks and earthworks.
Cropmarks occur where there are archaeological features, such as walls and ditches, underneath where a crop is growing. For example, greener healthier crops grow above ditches where there is more soil depth. The result is a plan (or birds-eye) view of the layout of features across a site.
Earthworks are banks, ditches and mounds of earth and stone. They cast shadows, which can show up in aerial photos.
Aerial photos are particularly useful because they often show more of an archaeological landscape than is visible from the ground.
This aerial photograph shows the negative cropmark of a Roman road (centre). It runs through the civil settlement outside the Roman fort at Raboienei in Romania. If you look carefully you can also spot the layout of some buildings. This photo was taken during an aerial photography project in Romania © W.S. Hanson