That is the quiet puzzle at the heart of this Co. Wicklow ringfort, a roughly circular earthwork sitting towards the southern end of a low ridge, surrounded by marshy ground that drops away gently to the east, south, and west. The ridge would have offered a modest elevation above the wetland, just enough to keep a household dry and to make the enclosure defensible without requiring the commanding hilltop positions that other ringforts favour.

A rath, as this type of site is sometimes called, is an early medieval farmstead enclosed by one or more earthen banks and ditches, a form that was widespread across Ireland roughly between the fifth and twelfth centuries. At Knockanarrigan, the circular enclosure measures thirty-two metres in diameter, defined by an earthen bank four and a half metres wide and between one and one point four metres high, with an external fosse, or ditch, three and a half metres across running around its outer edge. Three gaps break the line of the bank. The one to the north-east is only partly blocked and appears to preserve a possible causeway, which would have been the original entrance, allowing passage over the fosse. The gaps to the west and south read as later intrusions, probably the result of agricultural activity over the centuries. A field boundary running north to south cuts across the fosse on the eastern side, a reminder of how routinely later generations of farmers simply absorbed these ancient enclosures into the working landscape without ceremony. Inside the enclosure, in the eastern sector, a low circular platform roughly eight and a half metres across and about fifteen centimetres high may represent the remains of a hut foundation, the faint ghost of a structure where someone once lived, stored food, or sheltered animals through a Wicklow winter.