On the eastern bank of the River Liffey in Co. Kildare, a small circular feature lies invisible to anyone walking the surrounding grassland. No mound rises from the earth, no stones break the surface. The only way to see it is from above, and even then only under the right conditions: a dry summer and a satellite passing overhead at the correct moment.

The feature at Castlesize is a ditch barrow, a type of prehistoric funerary monument defined not by an upstanding earthwork but by a circular ditch cut into the ground, often surrounding a central burial. Over centuries, ploughing and weathering can level whatever mound once existed, leaving the ditch itself as the sole surviving trace. These buried ditches retain moisture differently from the surrounding soil, and during dry spells the grass or crops above them either stress or thrive in ways that betray the outline beneath. The result is a cropmark, a ghostly ring that appears in aerial or satellite photography when conditions align. The Castlesize example, roughly eleven metres in diameter, came to light in Google Earth imagery captured on 28 June 2018, when a dry period apparently drew the circular outline into visibility across the riverside pasture.