St. Mary's is Rostock's largest and most important church, first mentioned in a document in 1232. Transept and nave of the cruciform basilica are of equal length and emphasize the massive and closed impression. The church has precious furnishings, such as the oldest astronomical clock in northern Germany from 1472, which functions with original parts, and a bronze baptismal fountain from 1290.
The origins of St. Mary's Church are obscure. The first documented mention of a preacher at St. Mary's is in 1232. The first St. Marien church building was an early Gothic hall church with a vault height of about 15 meters and a simple gable roof, the wall connection of which can still be seen today on the east side of the church tower.
After St. Mary's was named the main church of the city of Rostock in 1265, this building was no longer sufficient to meet the demands of the citizens in the long run. Thus, in 1290, work began on expanding the church into a basilica based on the model of St. Mary's Church in Lübeck. The construction work lasted for more than one hundred years. Since 1440 the church and since 1796 the tower have had their present form.
Until the turn of the 19th/20th century, St. Mary's was a university church. Signs in the professors' pews still indicate this. For some years now, around the opening date of the university, the ceremonial matriculation of new students has taken place in St. Marien.
The extensive church library of St. Mary's was then transferred to the university library.
A special sight is the astronomical clock. This was created in 1472 by the clockmaker Hans Düringer, and the main clockwork still contains the original parts from that time. Both the main clock movement and the calendar movement and carillon, apostle walk and hour bell are wound daily by hand. In 1642 the clock was extended by the carillon, the apostle walk and the ornate Renaissance case. At the very top, six figures (evangelists and apostles) move in solemn procession past Christ, who stands in the center and blesses them, on an outstanding platform every day at noon and at midnight. At the same time, the carillon sounds every hour on the hour.