It is, in fact, a rath, one of the thousands of earthen ringforts scattered across Ireland, each one the remains of a farmstead enclosed for security and status, most of them dating to the early medieval period between roughly the fifth and twelfth centuries. What makes any individual example worth pausing over is the sheer persistence of the thing: two and a half metres of earthen bank, still standing, still defining a near-perfect circle after more than a thousand years of weather and grazing animals.

The enclosure at Letterscanlan measures approximately 23.5 metres north to south and 24 metres east to west, making it a modest but complete example of the type. Around its outer edge runs a fosse, the shallow defensive ditch that would originally have reinforced the bank, though it has been reduced over the centuries to little more than a faint depression. The bank itself is heavily overgrown, which is common enough on sites that have never been formally cleared or managed. There are two gaps in the circuit: one to the east, nearly ten metres wide, which may represent an original entrance, and a second to the south, around six metres across, that appears to be a more recent breach, perhaps opened at some point to allow livestock through. These interruptions give the structure a slightly incomplete look from ground level, though the overall form holds.