San Giovanni a Mare, popularly also known as San Giuseppe - church, standing in the center of Gaeta facing the port on Via Bosa. The current church building stands on the site of a small ancient chapel, which was destroyed during the earthquake 1213th year. Between the 15th and 17th centuries San Giovanni a Mare was decorated with frescoes and stucco decorations in the Baroque style (stucco). Then in the church there were a marble high altar and small altars of artificial marble. At the end of the 19th century the church was given to a small cell body of the Neapolitan school, which, unfortunately, in the 70s of the 20th century has been lost.

In the 20th century, the building of San Giovanni a Mare several times undergone reconstruction. Major restoration work was carried out here in 1928, the year when they were removed all the baroque decorations. And since 1998, the year up to the beginning of the 21st century, work was carried out to strengthen the structure of the building.

Simple gable facade of the church is crowned with a small bell tower with three arches, which contain the same amount of bells. In the center of the facade can be seen small round rose window, under which there is a portal with a gothic frescoed lunette. While the right-hand side of the church is inscribed in a residential area, the left side and the apse facing the small pedestrian area. On the left hand is seen the original dome of San Giovanni a Mare, decorated with small hanging arches and beautiful mosaics reminiscent of the Byzantine. On the back porch of the church you can see three of its apse.

Inside the temple consists of three naves, which is located in the center of the transept with a dome. The depth of each aisle is the apse: in the largest is the main altar, which is made of lining Christian sarcophagus reliefs 2-3 centuries. It is worth noting the strong slope of flooring made in order to avoid flooding the presbytery during high tide. On the walls of San Giovanni a Mare preserved fragments of frescoes from the 15th century.