A midden is, in essence, a prehistoric rubbish heap, an accumulation of shells, animal bones, ash, and discarded domestic material built up over generations of coastal habitation. Where grander monuments record ambition or belief, a midden records dinner.

Inis Doire sits within the layered island landscape of Clew Bay, an area with a long history of seasonal and permanent settlement. The presence of a midden on such a small island suggests that at some point, people were living here in sufficient number and for sufficient time to leave behind this kind of stratified domestic deposit. Shell middens in particular are valuable to archaeologists because the calcium in shellfish helps preserve organic material that would otherwise decay, meaning that fragments of bone, charcoal, and even worked flint can survive within them for thousands of years. They are found all along the Irish Atlantic coast, many dating to the Mesolithic period, though middens continued to accumulate well into the medieval era.