The Church of San Cesareo de Appia, mistakenly referred to as San Cesareo in Palatio, is a religious building located in Rome, in the Celio district, near Porta di San Sebastiano. Its very ancient origins date back to the 8th century and the remains of pre-existing Roman structures are still visible on the site, like a mosaic floor from the 2nd century AD that can be found in the basement. Throughout the centuries, this church underwent many transformations and was also called San Cesareo in Turrim, almost certainly because of its proximity to a high tower, and later also under the name San Cesareo in Palatio, causing its location to be confused with the church of the same name in the Campitelli district. In the 14th century, the church was left to the Crucifers to found a hospital for pilgrims and later to the Benedictine nuns. In the 16th century, the church was later restored by Cavalier d'Arpino and then entrusted to the Somaschi Priests, at the same time also transferring the 13th-century mosaics and other architectural furnishings that were in the Basilica of San Giovanni in Laterano, which was undergoing renovation at the time. The church has a simple façade, with an entrance door preceded by a portico with granite columns, as well as a single nave. Mosaics, artwork by Cavalier d'Arpino, depicting scenes from the life of St Caesar, are found on the sides of the windows, while the apsidal basin features a mosaic depicting God the Father among the angels. The altar, ambo, pulpit and transepts of the presbytery are architectural elements from the Basilica of San Giovanni, mostly composed of heterogeneous elements dating back to the 13th century. Lastly, the pipe organ in the Church of San Cesareo de Appia, built between 1997 and 1999 by Francesco Saverio Colamarino, has two keyboards with 61 keys each and a 32-note pedalboard, as a console, there is an electric organ that utilises the multiple register system.