The reason for that strange silhouette is buried inside it: the interior has been filled in to a depth of 3.6 metres, raising the ground level within the enclosure far above what it would originally have been. The working explanation is that generations of farmers used the hollow of the rath as a convenient dumping ground for field clearance, piling stones and debris inside until the interior effectively vanished.

A rath, sometimes called a ringfort, was the most common form of enclosed settlement in early medieval Ireland, typically consisting of a circular bank and ditch surrounding a farmstead. Most are described as univallate, meaning they have a single enclosing bank, as is the case here. The Tullaghna example has an internal diameter of around 25 metres, which is a fairly typical size. What makes it harder to read in the landscape is precisely that accumulated fill. The enclosing bank still rises between 1.6 and 2.6 metres above the surrounding land on the outside, but because the interior has been built up so dramatically, the difference in height between the bank and the ground inside it is only 0.8 to 1.6 metres. The proportions that would normally allow a visitor to intuit the original structure have been compressed and distorted. The site sits on a south-facing slope, which would have given whoever lived there a wide view over the surrounding land, a consideration that clearly mattered to the people who chose the location in the first place.