St. Marien, the former parish church, formed the core of the merchant town. It was consecrated on Bartholomew's Day in 1447. The late-Gothic, three-aisled hall church with hall choir and 82 m high double towers still testifies to the pride and wealth of the Stendal Hanseatic merchants. The most precious piece of the interior is a carved, twofold changeable Marienaltur from 1470. The choir stalls from 1500 are an Almärkische work. The choir screen from 1230, triumphal cross group from the 14th century, the Renaissance pulpit from 1566 and the organ as well as the bronze baptismal font from 1474 are further valuable pieces of the interior. Under the organ gallery there is a valuable, still functional astronomical clock from the 16th century. This type of clock is only found in Hanseatic cities. Another treasure of the church is the largest ring in the Altmark with 12 bells.
Two of the bells were cast in 1490 by the Dutch bell caster Gerd van Wou, who also created the "Gloriosa" in Erfurt Cathedral.
To the left of the entrance portal of St. Marien is a sundial on the supporting pillar.