It looks, at first glance, like a hollow-way, the kind of sunken track worn into the earth by centuries of foot and animal traffic. But this one carries a degree of ambiguity that makes it more interesting than that. Archaeologists have noted that it may not have been a road at all, or at least not primarily. Its position along the northern edge of a fortification's bailey, with a bank on its southern side acting as the enclosing boundary of that bailey, suggests it may have functioned instead as a defensive fosse, a ditch intended to define and protect the perimeter rather than to admit visitors.

The wider complex here began as a motte-and-bailey castle, a form of fortification introduced to Ireland by the Anglo-Normans, consisting of a raised earthen mound, the motte, with a flat-bottomed ditch at its base and a lower enclosed courtyard, the bailey, attached to one side. This particular example was originally constructed around 1214 by Henri de Londres, Archbishop of Dublin, on a ridge overlooking a marshy stream valley to the north. The site was later extensively rebuilt to serve as a base for campaigns against the O'Tooles, the Gaelic Irish family who controlled much of Wicklow at the time, and it was probably enlarged to its present form during that period. In an ironic turn, the site was subsequently granted to the O'Tooles themselves, before being destroyed at some point before 1636 and never repaired. What remains today includes the near-square motte with its steep rubble-faced sides and level summit, traces of an Anglo-Norman stone castle or gatehouse on the eastern portion, and the enigmatic sunken road that trails off eastward into the bog, its original purpose still not entirely settled.