San Marcos is a Gothic church in Jerez de la Frontera. It originates from one of the six parishes founded by King Alfonso X of Castile after his conquest of the city in 1264. The current edifice was likely started in the mid-14th century, due to the style of its polygonal apse and the Mudéjar portal, perhaps above a pre-existing mosque. The construction is anyway not documented until the middle of the 15th century, including a substantial renovation in late Gothic style.
The church has three façades, with a main entrance portal in Mannerist style (16th century). The interior has a Baroque high altar (18th century)
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.