A midden is, at its simplest, a refuse heap, the accumulated discards of people going about their daily business, most often shells, animal bones, charcoal, and broken pottery. What makes such deposits remarkable is precisely their ordinariness: they preserve not the monuments people intended to leave behind, but the traces they never meant to leave at all.

Middens are found along coastlines and beside inland water sources throughout Ireland, and their contents can span centuries of continuous or intermittent activity. Shell middens in particular, where the remains of oysters, limpets, periwinkles, and other molluscs accumulate in dense layers, can build up over remarkably long periods, and the alkaline environment created by the shells helps preserve organic material that would otherwise decay. The site at An Chrois is formally recorded as an archaeological monument, which places it within the broader pattern of such deposits identified across the west of Ireland, a region where coastal and estuarine resources were intensively exploited from the Mesolithic period onwards.