Santi Marcellino e Pietro ad Duas Lauros is a 20th century parish church on an ancient site at Via Casilina 641, in the Prenestino-Labicano district and near the Berardi metro station on the electric railway to Giardinetti (the future Linea C). It replaced a small 17th century church nearby on the same site.
The catacombs of the martyrs Marcellinus and Peter were established here about the year 300, and a basilica was built in the reign of Emperor Constantine together with the surviving Mausoleum of Helena (his mother) which is behind the present church. The mausoleum has the nickname Torpignattara because of the amphorae used in its construction which reminded bygone people of pinecones (pigne).
The layout of the complex was odd. The basilica was one of several in Rome of this period which had a circular far end which the nave arcades followed round and joined up to form an ambulatory behind the altar (a layout technically known as circiform). Each arcade had ten rectangular pilasters, and a further five of these formed the ambulatory. There was an inner narthex formed by two cross-walls connecting the first two pairs of pilasters in the nave, and this arrangement created a pair of square rooms at the near ends of the aisles. These walls were at a slight angle to the major axis of the church. The southern or left-hand room was the actual entrance, accessed by a long covered corridor which was one side of a large cloister. The opposite side of this cloister abbutted the basilica on the south side of the ambulatory.
East of this inner narthex was an outer narthex, which was one rectangular space with a wide entrance from the inner narthex matching the width of the main nave. This connected to the circular mausoleum through a surviving tall arched entrace, and the whole rectangular plan was at the same angle to the basilica as the cross-walls of the inner narthex.
It is thought that this complex was intended as the funerary monument of the emperor Constantine , before he founded the new city of Constantinople and hence passed it on to his mother.
The basilica fell into ruin in the 9th century, and vanished except for the mausoleum which apparently had already been turned into a fortress in the previous century. In the 11th century the sarcophagus of St Helena was taken to the Lateran (it is now at the Vatican), and this can be taken as the final cessation of any cultic activity on the site. The mausoleum was used as a little castle until 1638, when a small church was built within its ruins. This was enlarged as a parish church in 1765, still within the mausoleum. However, the complex was too small for modern needs and a completely new church was built in a neo-Romanesque style in 1922 on the site of the ancient basilica.
The church used to be the responsibility of the Canons Regular of the Lateran , but was given up to the diocesan clergy in 1936. It is now administered by the Congregation of the Charity Schools, which in Italian is known as the Instituto Cavanis.
The mausoleum has recently been thoroughly restored. It was hoped that this would include opening the catacombs to the public on a regular basis, but this does not seem to have happened.
The small, rectangular 17th century church peeps out of the entrance to the mausoleum rather like a hermit crab out of its shell. It was restored in 1769, 1779 and 1858 and narrowly escaped demolition in the early 20th century
It has a typical Baroque single-storey small church façade, with a pair of Doric pilasters holding up a triangular pediment. This is intruded upon by a large rectangular window above the entrance.
The interior had a single altar, with an anonymous 17th century altarpiece depicting Christ Venerated by Saints.
The new church is typically basilical in form, with a nave and aisles and a single pitched and tiled roof covering both nave and presbyterium. The roofs of the aisles are flat. There are no transepts, and no campanile.
An internal entrance loggia of three arches in white stone occupying the width of the nave façade is flanked by two blind arches of the same dimensions forming the ends of the aisles. The arches are separated by Doric columns, and four doubled Corinthian pilasters occupy the façade corners and the ends of the arcade. The first storey is topped by an entablature which runs along the aisle rooflines. The second storey has a central window with a segmental pediment, flanked by a pair of empty round-headed niches. This storey is topped by an empty triangular pediment. The church fabric is rendered in pale orange with white detailing.