At Coolroe in County Kildare, the outline of an ancient enclosure and the traces of a possible field system lie entirely out of sight at ground level, legible only from the air. The land holds its secrets in the form of cropmarks, the subtle differential growth of crops over buried ditches and banks that briefly becomes visible in dry summers when aerial photographs are taken at the right moment.

The site came to light during aerial photographic surveys carried out by Dr. Gillian Barrett in 1989 and 1991. The photographs revealed the cropmarks of an oval enclosure defined by a fosse, which is essentially a wide ditch forming part of a boundary or defensive perimeter. On its eastern and northern sides, the enclosure appears to be abutted by what may be a field system, suggesting that the two features were in some way related, whether in date or in function. Cropmark evidence is inherently provisional; the shapes that emerge from aerial photography indicate where the ground has been disturbed or organised, but cannot on their own confirm the age of a feature or precisely how it was used. Even so, the combination of an enclosed oval form and adjacent field boundaries hints at a pattern of organised land use that would not be unusual in early medieval or prehistoric Ireland, though the record does not attribute a specific period to the Coolroe site.