At Brewel in County Kildare, a shallow groove in the earth, barely thirty centimetres deep and ten metres wide, traces a line roughly 130 metres across a gently sloping field. On its own, it would be easy to dismiss. But this inconspicuous hollow is understood to be a cursus monument, one of the more enigmatic categories of prehistoric earthwork found in Ireland and Britain. A cursus consists of two parallel ditches, or fosses, enclosing a long rectangular corridor of ground, typically closed at one or both ends. Their purpose remains genuinely unknown; they predate most of what we associate with organised prehistoric society, and theories range from processional routes to territorial markers to alignments with celestial events.

The Brewel example came to attention through cropmarks visible on a Google Earth image from April 2011, passed on by I. Kenny. Cropmarks form when buried ditches or banks affect the moisture and nutrients available to plants above them, producing variations in colour or growth that become legible from the air, particularly on freshly cultivated or re-seeded ground, as was the case here. The monument runs roughly northwest to southeast, level at the southeastern end and rising gently toward the northwest, where it terminates in a curved end. What gives it particular interest is its apparent orientation: viewed from the northwestern end and looking southeast along its axis, the cursus lines up with Keadeen Mountain and Brusselstown Ring, a hillfort on the same ridge. There is also a second cursus monument recorded on the slopes of Keadeen itself, raising the possibility that these features were deliberately placed in relation to one another, or to the mountain, across a prehistoric landscape that we can only partially reconstruct.