This multi-vallate hillfort consists of up to five concentric enclosures, each marking different phases of ancient defensive construction. The innermost enclosure, known historically as 'the Round O' on Victorian maps, forms an oval measuring 50 metres by 45 metres, defined by an earth and stone bank with both internal and external ditches. The dry stone facing visible today was likely added much later, but the core structure dates back thousands of years.

The hillfort's true scale becomes apparent when considering its outer defences, which stretch far beyond the central enclosure. The second rampart sits just above the 900-foot contour line, enclosing an area roughly 450 metres north to south and 400 metres east to west. A third defensive line once existed 150 metres further out, though only fragments survive today as field boundaries. Recent LiDAR mapping by archaeologists from University College Cork revealed a possible fifth enclosing element, pushing the total enclosed area to over 84 hectares and making this one of Europe's most impressive Iron Age fortifications.

Sample excavations conducted in 2015 by Professor William O'Brien confirmed the site's archaeological significance, uncovering evidence of substantial stone defences and traces of ancient occupation including burnt spreads and coarse pottery. The presence of additional archaeological features, including a hut site and ring barrow, suggests this was not merely a fortress but a complex settlement that dominated the Wicklow landscape for centuries. Today, the forestry plantation that covers most of the site ironically helps preserve these ancient earthworks, protecting them from modern agricultural damage whilst keeping one of Ireland's most important prehistoric monuments largely hidden from view.