Oratorio del Caballero de Gracia is one of the best hidden architectural treasures in Madrid. This church looks small from the outside, but inside it unfolds into a neoclassical temple by Juan de Villanueva, which looks like a Roman basilica.
Among its most noteworthy internal features are the single-piece granite columns, the vault and the sculptures of the Virgen del Socorro, signed by Francisco Elías in 1825, and of Cristo de la Agonía, which, according to studies, was made by Juan Sánchez Barba in 1650. The church belongs to the Caballero de Gracia Eucharistic Association, founded by Jacobo Gratiis (known as the Caballero de Gracia), who was born in Modena in 1517 and who died in Madrid in 1619. It is currently run by Opus Dei.
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.