At Tully in County Kildare, a low mound of earth and stone sits on a gentle hill from which the land opens out in every direction. It is a modest thing now, roughly two metres high with a base diameter of eleven metres tapering to a flattened upper surface of just one metre across, but its position is deliberate and its origins are older than any map that has recorded it.

By the time the first edition of the Ordnance Survey six-inch map was published in 1838, the mound had already been co-opted into more practical purposes. The surveyors marked it as a trigonometrical station, one of the fixed points used to calculate the precise geometry of the landscape, sitting at an elevation of 387 feet above sea level. The choice was logical: the elevated, unobstructed position that made the mound useful to whatever society first raised it also made it ideal for the theodolites of the nineteenth century. At that point it appeared as a circular area of roughly 25 metres in diameter, ringed by trees. By 1972, however, the picture had changed considerably. A site record from that year described the mound as very much defaced and poached by livestock, the surface broken and worn. It had been fenced off by then to prevent further deterioration, and what survives today is a reduced but still legible earthwork, the kind of quietly persistent feature that tends to outlast most of what surrounds it.