St. Mary's Church, or formally the Basilica of the Assumption of the Blessed Virgin Mary, is a Brick Gothic Catholic church located in central Gdańsk, Poland. With its volume between 185,000 m3 and 190,000 m3 it is currently one of the two or three largest brick churches in the world.

Between 1536 and 1572 St. Mary's Church was used for Catholic and Lutheran services simultaneously. From the 16th century until 1945 it was the second largest Lutheran church in the world.

According to tradition, as early as 1243 a wooden Church of the Assumption existed at this site, built by Duke Swietopelk II.

The foundation stone for the new brick church was placed on 25 March 1343, the feast of the Annunciation. At first a six-span bay basilica with a low turret was built, erected from 1343 to 1360. Parts of the pillars and lower levels of the turret have been preserved from this building.

In 1379 the Danzig architect Heinrich Ungeradin and his team began construction of the present church. Their building shows some differences from St. Mary's Church in Lübeck, sometimes called the mother of all Brick Gothic churches dedicated to St. Mary in Hanseatic cities around the Baltic, and it has some details in common with Gothic brick churches in Flanders and the Netherlands. By 1447 the eastern part of the church was finished, and the tower was raised by two floors in the years 1452–1466.

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