The example at Cullagh More in County Sligo is one such site, a low crescent-shaped heap of fire-cracked stone and dark, charcoal-flecked earth that would be easy to walk past without a second glance. Burnt mounds, known in Irish as fulachtaí fia, are generally dated to the Bronze Age, and the prevailing theory holds that they accumulated beside a water source as stones were heated in fire and then plunged into a trough to boil water. What that water was used for, whether for cooking, bathing, hide-working, or brewing, remains a matter of genuine debate among archaeologists.