It is a fulacht fia, and that vagueness is, in its own way, appropriate. These sites, found in their thousands across Ireland, are among the most common and least understood monuments in the Irish landscape. They are the remains of prehistoric cooking places, or possibly brewing sites, or perhaps both: a trough would have been dug into waterlogged ground, filled with water, and heated by dropping fire-cracked stones into it. Over time, the shattered, blackened stones were raked aside into a mound, and it is those mounds, often horseshoe-shaped and frequently found near water, that survive today.

The Aglish example sits in precisely the kind of location that fulachtaí fia tend to favour: low, wet ground close to a water source. The combination of marshy terrain and centuries of vegetation has left the mound in a state where even its basic size is unclear, which is not unusual for sites of this type. Most fulachtaí fia date to the Bronze Age, roughly 1500 to 500 BC, though some have produced earlier or later dates. They are rarely dramatic to look at, being essentially modest humps in the ground, but their sheer number across the Irish countryside speaks to a society that returned repeatedly to the same practical method of heating water over many generations.