It was built to a simple rectangular plan, with the nave and chancel probably divided by rood screen, over which was a rood loft lit by a window high in the south wall. A narrow doorway led to a vestry or sacristy, and the interior was plastered and painted. At this time the sea would have been some distance off, with plenty of space for a burial ground on all sides of the church: today the sea batters against the north wall of the church. However, during the period of the Lordship of the Isles most of the West Highland chiefs were buried at Iona in the lay cemetery of Reileig Oran, so it was probably not envisaged originally as a resting place for the clan chiefs.
The church was dedicated to Saint Columba, the founder of the great 6th century abbey at Iona, who is credited in large part with the Conversion of Scotland. Many churches built in the later Middle Ages had this dedication.
Eaglais na h-Aoidhe underwent alterations in the 15th and earlier 16th centuries, and several periods of work can be distinguished in its masonry. The Macleods of Lewis started to use the chancel as a place of burial, and the church took on its final form with the additional of a burial aisle at the west end. The most celebrated of the graveslabs within the church is probably that of Roderick Macleod, VII of Lewis. He held Lewis during the latter part of the 15th century, and was the father of Torquill VIII and grandfather of John Mackinnon, the last abbot of Iona.
Roderick died in 1498, and is commemorated on his graveslab as a warrior, with broadsword and spear, and dressed in a helmet, mail 'collar' and quilted body-armour.
For many years the church has stood as a roofless and increasingly unstable shell, but the long process of re-roofing and restoration is underway, championed by the local community.
This may not have been the first church on the site. A local tradition maintained that 'the church was built on the site of a cell occupied by St Catan, who is believed to have lived in the sixth or seventh century' (W.C. Mackenzie, 1919). Catan was an early Irish saint, who became bishop of Bute, and chapels dedicated to him can be found scattered throughout many parts of Scotland. It is likely that Catan, or some of his followers, established a small chapel in the area, of which no trace now is known. However, the footings of an early chapel survive at Taigh an t-Sagairt, 4 kms to the south-east.
Before any ecclesiastical presence on the site, people had been living and working there over several millennia: midden deposits containing winkle, limpet and mussel shells, fishbones, animal bones and stone tools are exposed from time to time along the shore, and over the years these deposits have built up to more than 2m in height below the foundations of the church. Not far from the church, remains of a small late Iron Age building with an earth floor, stone walls and a hearth were found in 1937, associated with more pottery and animal bones.