The site, known to archaeologists as LA035-016001, appears as cropmarks; subtle differences in plant growth that trace the foundations of long-vanished structures. When viewed from above, particularly in photographs taken by the Cambridge University Collection of Aerial Photography in the mid-20th century, the marks reveal part of a subrectangular enclosure alongside what appears to be a circular enclosure.

These cropmarks form when buried archaeological features affect the growth of crops above them. Where ancient ditches once ran, the deeper, moister soil produces lusher growth, whilst stone foundations or compacted earth create patches where plants struggle to thrive. The result is a pattern visible only from the air, like a photographic negative of the past printed in wheat or barley. At Grenan, these telltale signs suggest a complex site that may have served multiple purposes; the rectangular enclosure possibly indicating a farmstead or defensive structure, whilst the circular feature could represent anything from a ringfort to a ceremonial space.

Today, nothing remains visible at ground level; centuries of ploughing and weathering have erased any surface traces of these ancient structures. The site’s existence is preserved only in these aerial photographs and in the Archaeological Inventory of County Laois, compiled in 1995 by P. David Sweetman, Olive Alcock, and Bernie Moran. Without the bird’s eye view provided by aerial archaeology, this piece of Ireland’s hidden history would remain completely unknown, buried beneath the seemingly empty fields of the Laois countryside.