A midden is, in essence, an ancient rubbish heap, a place where people discarded the remains of meals, most often the shells of oysters, mussels, periwinkles, or other shellfish, alongside animal bones, broken pottery, and other domestic debris. That description makes them sound mundane, but middens are precisely what archaeologists value most: unguarded, accidental records of how people actually lived, ate, and worked along a coastline.

Acaill Bheag sits in the shadow of Achill Island, the largest island off the Irish coast, and the waters around this part of Mayo have supported human settlement for thousands of years. Coastal middens in Ireland range in date from the Mesolithic period onward, some of them representing seasonal camps where hunter-gatherers returned year after year to harvest the sea. Without more specific dating information for this particular deposit, it is difficult to say with confidence where in that long sequence this midden falls, but its presence on such a small island speaks to the degree to which these outer islands were once regularly used, whether for fishing, fowling, grazing, or simple shelter from the mainland.