Santi Marcellino e Pietro al Laterano is dedicated to Saints Marcellinus and Peter, 4th century Roman martyrs, whose relics were brought here in 1256. The first church on the site was built by Pope Siricius in the 4th century, close to the Via Labicana's catacombs of Marcellinus and Peter, with an adjoining hospice which became a centre for pilgrims.
This church was restored by Pope Gregory III in the 8th century. In the 9th century, the remains of Saints Marcellinus and Peter putatively were transferred from the catacombs here to a church in Seligenstadt, Germany. When the church was rebuilt in 1256 by Pope Alexander IV, the martyrs' relics were putatively returned.
At Present, under the high altar is an urn containing relics of Saint Marcia. On the left side is an altar dedicated to the Blessed Virgin, with a copy of Guido Reni's The Virgin in Glory with Angels, St Joseph and St Rita. Next to it is the Chapel of Reconciliation. An image of the dedicatees was placed on the first column on the left from the entrance during this restoration, with an inscription recording the restoration. The hospice and church were then given in 1276 to the Confraternity of those Commended to the Saviour.
The present church is the result of Pope Benedict XIV's 1751 reconstruction. The present cube-shaped exterior is divided by pilaster strips in a Neoclassical style, but with a late-Baroque elements, including a dome influenced by the architecture of Borromini. The façade was designed by Girolamo Theodoli and the main altarpiece by Gaetano Lapis depicts the dedicatees' martyrdom. After that restoration, the church was awarded until 1906 for the worship of the Discalced Carmelites.
References:The Church of St Donatus name refers to Donatus of Zadar, who began construction on this church in the 9th century and ended it on the northeastern part of the Roman forum. It is the largest Pre-Romanesque building in Croatia.
The beginning of the building of the church was placed to the second half of the 8th century, and it is supposed to have been completed in the 9th century. The Zadar bishop and diplomat Donat (8th and 9th centuries) is credited with the building of the church. He led the representations of the Dalmatian cities to Constantinople and Charles the Great, which is why this church bears slight resemblance to Charlemagne's court chapels, especially the one in Aachen, and also to the Basilica of San Vitale in Ravenna. It belongs to the Pre-Romanesque architectural period.
The circular church, formerly domed, is 27 m high and is characterised by simplicity and technical primitivism.