Marientor, Medieval city gate in Naumburg, Germany.

The Marientor is a medieval city gate with a double archway structure positioned at the junction of Marienstrasse and Postring. The construction features two gate openings arranged in sequence, creating a passage design typical of medieval town fortifications.

The gate dates to the medieval period and was once part of the fortification system protecting the city. It remains one of the few surviving town gates from that era, demonstrating the former importance of the city's defenses.

The gate's name probably comes from the nearby Marien-Magdalena-Kirche or from the Marienfigur in its niche, carved by Peter Hummelshain of Naumburg in 1456 and later given a wooden boy. Since 1997–2000 restoration the interior houses an exhibition on Naumburg's town fortifications, and the gate serves as a puppet theatre of Theater Naumburg and as a backdrop for open-air events.

The gate stands in the northeast of the old town, where Marienmauer, Postring and Marienstraße meet. The tower can be climbed and the exhibition on the town fortifications in the gate building can be visited from late March to early November.

The inner courtyard is a Fanghof, or trap yard: the late-Gothic parapet walk has openings for firing inward as well as outward, so attackers who got past the outer gate could be shot from above. The gate also served as a prison between the 16th and 19th centuries.