The one at Ballynultagh in County Wicklow complicates that expectation, because attached to the western edge of a ringfort here is a D-shaped annexe, a secondary enclosure whose curved bank and external fosse are not separate constructions but direct continuations of the defences surrounding the main fort. The northern outer bank of the ringfort carries straight on to form the northern boundary of the annexe as well, giving the whole complex an interlocking, almost architectural logic.

A ringfort, broadly speaking, is a circular or near-circular enclosure defined by one or more earthen banks and ditches, the characteristic farmstead form of early medieval Ireland, roughly from the fifth to the twelfth centuries. An annexe attached to such a fort is less common; it is generally interpreted as a supplementary enclosure, possibly used to shelter livestock, store goods, or provide a controlled approach to the main dwelling. Here the annexe measures roughly 35 metres north to south and 25 metres east to west, while the overall complex extends to around 84 metres east to west and 56 metres north to south. The banks are built from earth and gravel, standing about 0.9 metres high and roughly 3 metres wide, with an external fosse, that is, a ditch running outside the bank rather than within it. The site sits on a gently eastward-facing slope at the edge of a ridge, with the ground falling away sharply to the north, a positioning that would have given its original occupants a natural advantage in terms of drainage, outlook, and passive defence. A gap of nearly four metres in the western bank of the annexe is of modern origin, likely cut to allow agricultural access at some point after the site fell out of its original use.