They appear as low, horseshoe-shaped mounds, typically found near water, and are generally dated to the Bronze Age, roughly 1500 to 500 BC. The one at Ballylahan in County Mayo is a quiet example of a site type that archaeologists have puzzled over for decades. The name translates loosely from Irish as something like "cooking place of the deer," and the dominant theory holds that they functioned as outdoor cooking sites: a trough filled with water was brought to the boil by dropping fire-heated stones into it, and the cracked, discarded stones accumulated over time into the characteristic mound that survives today. Some researchers have proposed alternative uses, including bathing, brewing, or textile processing, and the debate has not been fully settled.

Ballylahan itself is a townland in the east of County Mayo, an area with a layered prehistoric and medieval past. The presence of a fulacht fia here fits a broader pattern across the west of Ireland, where Bronze Age communities left traces in the landscape that only became legible to modern eyes through systematic field survey. Without more detailed records currently available for this particular site, the specifics of its dimensions, condition, and precise location within the townland remain difficult to pin down, but its existence in this part of Mayo is itself a small reminder that the land was well used long before any written account of it survives.