A field system is exactly what it sounds like, an arrangement of boundaries, enclosures, and divisions laid out across the ground, but the phrase does little justice to what such features can represent. In Ireland, field systems range from the extraordinary Céide Fields of County Mayo, preserved beneath blanket bog for over five thousand years, to post-medieval networks of lazy beds and stone walls that speak to more recent, and often grimmer, histories of land use and tenure. The one at Castletown has been formally recorded as an archaeological monument, which means someone, at some point, judged its boundaries old enough or significant enough to warrant protection.

Field systems are among the more quietly eloquent monuments in the Irish landscape. Unlike a tower house or a passage tomb, they do not announce themselves. They ask the eye to read the ground, to notice where a ridge runs slightly proud of the surrounding earth, or where a line of stones persists along a boundary that no longer serves any practical purpose. In Connacht particularly, the evidence of pre-Famine settlement and cultivation survives in remarkable density, and field boundaries can sometimes be traced back through several distinct phases of use, each overlaying the last. Without more specific detail available for this particular site, it is not possible to say whether the Castletown system is prehistoric, early medieval, or of more recent origin, but the fact of its survival and recognition is itself worth noting.