A cashel is a type of ringfort built from stone rather than earth, its boundary formed by a circular dry-stone wall rather than a raised bank and ditch. Where earthen ringforts are the more common sight across Ireland's midlands and east, cashels tend to cluster in the stonier west, where the raw material was simply what the ground offered. They date broadly to the early medieval period, roughly the sixth to the twelfth centuries, and served as enclosed farmsteads for families of varying status, the scale and thickness of the wall often reflecting the wealth of whoever built it.

Fauleens is a small townland, and the cashel it contains belongs to a category of monument that numbers in the thousands across Ireland, yet each one represents a specific decision made by specific people to enclose a particular piece of ground. The word cashel itself derives from the Irish caiseal, cognate with the Latin castellum, and was borrowed into the language long before the Norman arrival. Most cashels were never fortified in any military sense; they were working enclosures, protecting livestock and household from wolves and opportunistic raiders rather than organised armies. The Fauleens example, sitting in the west Mayo countryside, is one of many such structures in the region that have endured largely through the accident of being built from stone, which outlasts the earthworks of comparable sites elsewhere.