Some places earn their place in the record precisely by disappearing. At Knockavannia in County Waterford, a ringfort, the type of circular earthen enclosure built throughout Ireland during the early medieval period, typically as a farmstead or defended homestead, once sat towards the top of a north-west facing slope in rough pasture. It was recorded on Ordnance Survey maps in both 1840 and 1927, measuring roughly fifty metres in external diameter on the earlier map and around sixty metres on the later one. By 1973 it had been removed entirely, and today nothing of it is visible at ground level. The site persists in the record only as an absence.

The slight discrepancy in the diameter measurements between the two OS editions is quietly interesting. Whether that reflects actual change to the earthwork over the intervening decades, differences in survey technique, or simply the difficulty of measuring a degraded feature in rough pasture, is impossible to say now. What is clear is that the enclosure was still considered significant enough to mark in 1927, and was gone within a couple of generations. Archaeological testing carried out in 2004 in the adjacent townland of Kilkeany, roughly sixty metres to the north-west, failed to produce any material that could be connected to the site, leaving its history without further elaboration.