The Cathedral of the Immaculate Conception in Sligo was developed by Bishop Laurence Gillooly who had been appointed Bishop of Elphin in 1858. He decided that the diocese was now of a size and wealth that the time had come to replace St. John's Parish Chapel, which had been recognised as the diocesan pro-cathedral.
He engaged George Goldie, one of the foremost Catholic architects in England in the nineteenth century. The cathedral was opened for divine worship on 26 July 1874 by Cardinal Paul Cullen of Dublin.
Modelled on a Normano–Romano–Byzantine style, it is the only example of a Romanesque style cathedral built during the 19th century. Designed in the shape of a basilica, the church has a square, pyramid-capped tower, which reaches a height of 70 metres, and supporting turrets at the west end. The circular baptistery incorporated in the apse with its five lancet windows behind the high altar, was originally designed as a mortuary chapel.
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.