It is a fulacht fia, a type of prehistoric cooking or processing site found in enormous numbers across Ireland, typically dating to the Bronze Age. The usual interpretation is that stones were heated in a fire and then dropped into a water-filled trough, bringing the water rapidly to a boil; the crescent-shaped mound that survives is the accumulated debris of shattered, fire-cracked stone discarded over repeated use.

What makes the Charlesfield example quietly notable is not any singular feature but its pairing. A second fulacht fia lies roughly sixty metres to the south, suggesting this patch of wet ground was visited and used on more than one occasion, perhaps across a long stretch of time, or by different groups returning to a landscape that suited the purpose. The marshy setting is characteristic; fulachtaí fia are consistently found near water sources, which were essential to the whole process. The mound here measures 7.9 metres in length and 9.4 metres in width, placing it within the typical range for this monument type, and the low profile of 0.35 metres reflects both the modest accumulation of material and centuries of natural settling and overgrowth.