Although the building is currently a Romanesque church (a style typical of the medieval period) it was probably originally erected as a Byzantine church in the 7^th century AD. The church stands on the very spot traditionally believed to be the site of Sant’Efis martyrdom, the place where his remains were buried and where they remained until they were transferred to Pisa (and eventually returned to Sardinia in 1886). The ancient sanctuary, called martiryum, was presumably located in the small domed room, now incorporated in the crypt.

The entire structure features very simple lines, built of sandstone and limestone blocks, which certainly came from the buildings at the nearby site of Nora or from the tophet from the Punic period (6^th -4^th century B.C.) that stood a few metres away. In fact, a funerary stele from the tophet is walled into the southern side of the church.

A large part of the outer wall face is exposed stone, while the façade is plastered. The latter is preceded by an atrium with a portico, added in the Spanish era between 1600 and 1700. The interior has a rectangular plan and is divided into three barrel-vaulted naves characterised by pillars supporting round arches. The small east-facing apse is of circular shape.