It takes a gas pipeline to find a prehistoric kitchen. That is more or less what happened at Ballyvass in County Kildare, where a routine excavation ahead of a Bord Gáis pipeline development uncovered a fulacht fia, one of the most common yet persistently mysterious monument types in the Irish archaeological record. Fulachtaí fia are ancient cooking or processing sites, typically identified by a mound of fire-cracked stone alongside a trough that could be filled with water and heated by dropping in stones made red-hot in a nearby fire. They are found in their thousands across Ireland, usually in low-lying, boggy ground near a water source, and they date mainly to the Bronze Age, though their exact function is still debated by archaeologists.

The 1999 excavation by Gregory (carried out under Licence No. 99E0453) revealed three shallow pits and two complete troughs at Ballyvass, with the site continuing southward beyond the initial dig, where the northern edges of two further pits were also uncovered. All the pits shared a consistent character: a primary layer of ash at the base, topped with charcoal-rich soil mixed with burnt stone, the accumulated debris of repeated heating and cooking episodes. Two flint scrapers turned up in one of the southern pits, a reminder that stone tools were still in use alongside the fire-and-water technology of the troughs. The troughs themselves differed from one another in instructive ways. One was a steep-sided oval cut directly into the natural subsoil, open and functional in its simplicity. The other was circular and more deliberately engineered, lined with redeposited natural subsoil, a material chosen because its relatively impermeable quality helped the trough hold water, the essential ingredient for the whole process to work. That small distinction, one trough relying on the cut alone, the other carefully waterproofed, hints at the practical thinking of whoever built and used the site.