St. John's Church (Sint-Janskerk), named after St.John the Baptist, was originally built as a baptistery for the St. Servatius Chapter of Maastricht. In 1633, after a period in which it functioned as an autonomous parish church, it came into the possession of the Dutch Reformed Church, established in 1632. This as a result of the capture of Maastricht from the Spanish army in 1632 by the troops of the Seven United Provinces of the Netherlands under the command of Prince Frederik Hendrik of Orange. After the establishment of a state-church, i.e. the Dutch Reformed Church, all catholic churches had become protestant in the regions already conquered.
The Prince Bishop of Liège, the Duke of Brabant and Prince Frederik Hendrik agreed that in Maastricht in principle only smaller chapels should be handed over to the protestants. The bigger churches remained catholic, which was exceptional from a national point of view. However, already in 1633 the protestant chapels proved to be too small and after new discussions two churches, one of which was St.John's, came into the possession of the protestants. The first service of the Dutch Reformed Church took place on the 1st of January, 1634.
Since 1987 the church has been in the use of the 'Protestantse Gemeente St. Jan', a federation of two different reformed communities.
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.