The entrance of the church is preceded by a marble portico built in the 16th century. Next to the church, on the right side of the portico, stands a round bell tower dating from the 9th or 10th century.

Originally built as Theodoric's palace church and dedicated to the Saviour, it was rededicated to St Martin of Tours during the episcopate of Agnellus (556-569) and finally to St Apollinaris in the 9th century, probably after the saint's relics were translated there in 856. It is a standard western basilica with a nave and two aisles, an apse and arcaded colonnades. The sumptuous mosaics reflect the dominant role that mosaics had assumed in the churches of the Christian East; the architecture is subordinate. One of eight Ravenna sites on the UNESCO World Heritage List.