The Church of St. Similien is an ancient church in Nantes. After the death of Bishop Similien in 310 AD, his successor, Eumilius, erected over his grave a votive chapel. One hundred years later, the bishop Leo, a Greek (444-458) built a real church to the site. In 848 AD, Nantes was vandalized during the Norman invasions. In 958 the restoration of the building began and was completed towards 1172 by the Duke Geoffroy II.
Following the siege of Nantes by Louis XI in 1487, Bishop Peter of Chaffault, repaired and enlarged the basilica Building it in the form of a Latin cross. The apse is Merovingian but the nave was extended towards the west, and flanked by two crosses.
During the French revolution, the church was closed to worship in 1793 and reopened after the Concordat of 1802. In 1824, the Millennium old building was destroyed and a church with three naves replaced it. The façade and portico were completed in 1835.
Fifteen years later, in 1850, the parish priest and the Church Council were considering the construction of a new church. In 1869, an architect, Eugene Boismen was appointed. The plans he offers were a Gothic building, inspired by those of the first half of the thirteenth century. The north-west facing building will include three naves, two ambulatory, bedside with a chapel which will be placed Our Lady of Mercy. The nave of five bays and end with a facade with two arrows. Permission to build the new church in 1872 is given. The Bishop Félix Fournier blessed the first stone of the new sanctuary on 5 October 1873. The work was completed in 1894 but as early as 1880, the vaults of the apse, the choir and transept were completed.
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.