The place-name itself is the giveaway: cill, the Irish word for a church or monastic cell, paired with the name of a saint, pointing to an early Christian foundation whose physical boundaries once shaped the life of the community around it. Ecclesiastical enclosures of this type, typically defined by a roughly circular or oval bank and ditch, were the standard way of marking out sacred ground in early medieval Ireland, separating the spiritual precinct from the secular world beyond its edge.

Cill Éinne is associated with Saint Enda, one of the most significant figures in early Irish monasticism. Enda is traditionally credited with establishing a monastery on Inis Mór, the largest Aran Island, sometime in the late fifth or early sixth century, and the site is regarded as one of the earliest monastic foundations in Ireland. The island's austere limestone landscape, its relative remoteness, and the discipline Enda was said to impose drew students and later saints to train there, including, according to tradition, Ciarán of Clonmacnoise and Brendan of Clonfert. What survives above ground today is a layered accumulation of centuries, with the enclosure boundary representing the oldest organisational logic of the site, predating or underlying much of what was built within it later.