The largest excavation undertaken during the season of 2005 in the Vrina Plain, at the ancient site of Butrint, centered on the 5th-century basilica, which was initially identified in 2004. It is clear that this church, with its mosaic pavement, was made within the ruins of earlier structures. In particular, a large Roman apsidal building was converted to form the entrance, or narthex, of the church. The apsidal building may originally have functioned as a triclinium belonging to a Roman domus. This in turn appears to be a development of an earlier Roman town house and associated bath-building, extending across a former road to form a single complex. By the 3rd century AD the building probably performed a public role as a place of storage, possibly as an agrarian depot, with a new triple doorway cut through its northern wall to give access to the waterfront.
A cataclysmic event destroying the structures across the Vrina Plain appears to have occurred some time in the 3rd century AD, and by the time of the creation of the church the apsidal building had been abandoned for almost two centuries.
The church itself comprises a large nave with an apse, a raised chancel, flanking aisles and a two-storey narthex. The elaborate mosaic which covers the entire floor of the church in a unified design was laid around AD 475-500, dated by three coins found in the supporting surface for the mosaic. The nave design comprises a rectangular grid of octagons filled with an abundance of animals, fruits and flowers. These are set around two tablets (tabulae ansatae) inscribed in Byzantine Greek. The best preserved of these, near the entrance, translates as “In fulfilment of the vow of those whose names God knows”. The other includes the words “ … and rest … your bodily substance …” with images of sheep and birds facing the inscription. The disposition of the motifs is somewhat informal, but a progression is notable from sea-creatures, terrestrial beasts and domestic birds, ordered groups around the inscriptions, culminating in an image of a large chalice (kantharos) denoting the Eucharistic space around the altar. The chancel mosaic is more varied in design and includes an arch flanked by trees and surmounted by two birds, within it is a red flower and a burning lamp. The chancel design may denote the presence of relics and hence the martyrial status of the church.
It is not certain precisely how long the church remained in use, but it seems that rising groundwater tables played a part in its desertion by the 9th century AD. Postholes cut through the mosaic floor demonstrate the need for props in an unstable building. There is evidence of industrial activity in the former narthex and graves were cut into the nave, connoting the continued recognition of the place.
In the mid mid-9th century AD it appears that the raised narthex building may have become the seat of new activity, possibly a fair. Two rare Byzantine lead seals show that the produce from here was formally managed by state officials.
From the rich black earth overlying the site, the excavations revealed some forty Byzantine coins, plenty of southern Italian pottery and abundant animal bones. As in the case of the church excavated at Diaporit, this basilica was stripped down in the 13th century probably to provide the flourishing city port of Butrint with materials for the ring of churches.