Exterior

The church is located on a relatively isolated position, a few meters from the coast. The main pavement is at some 5 meters above the external ground level, as the nave and the two aisles are built above a crypt corresponding to the original church.

The façade is accessed through a double staircase, at both sides of the Romanesque-style portal, leading to a gallery; the portal, within a blind arcade, has a decoration with some influence from Islamic art. The central bronze door was executed by Barisano da Trani in 1175; the original piece is now inside the church, while the external one is a replica made in 2012.

The façade is completed by three windows and a small rose window above the nave. They are decorated by animal figures.

The transept, facing the sea, has three apses, and also features blind arcades in Romanesque style. The side façades are also decorated with blind arcades and, on the southern side, by two mullioned windows and a rose window, while the northern side as two double and one quadruple mullioned windows.

The bell tower, standing at 59 m, was mostly built in 1230–1239, although the floors above the second one were completed only in the 14th century under bishop Giacomo Tura Scottini.^[1] As is typical in Romanesque structures, the openings (in the shape of mullioned windows) become wider in the upper floors.

The ground floor of the bell tower has an internal, ogival arcade creating a passage under it. The bell tower was completely dismantled and rebuilt in the 1950s to avoid it falling down.^[2]

Interior

The church plan has a nave and two aisles, separated by double columns that support two side matronaei. The aisles have cross vaulted ceilings, while the nave has nude trusses. The transept has also similar trusses.

The interior has lost much of its decoration, leading to the current largely bare appearance. In particular, the restoration in 1939-1942 mostly left only the medieval elements, removing later additions such as the painted wooden ceiling of the nave and the transept.^[3]

Only part of the original mosaics of the pavement, inspired by those of the Otranto Cathedral, remain in the presbytery area. These include scenes such as the allegory of Alexander the Great flying to heaven (see below) and the original sin episode with Adam and Eve.^[4]

The lower church, located under the main pavement, is divided into two main spaces: the Crypt of St. Nicholas, housing the saint's relics, and that of St. Mary. The lower church has a similar plan that the upper one and has Romanesque-style capitals. A small stairs leads to the hypogeum of St. Leucius, located below the sea level and decorated with frescoes in poor state of preservation.