Rententurm, Gothic defensive tower at Main River, Frankfurt, Germany.

The Rententurm is a Gothic defensive structure on the Main River in Frankfurt with four stories and a square floor plan. The structure is marked by four corner towers and a pointed spire that rises at the harbor entrance.

The tower was built between 1454 and 1456 under Eberhard Friedberger's direction and served to monitor ship traffic and collect taxes from vessels entering Frankfurt's harbor. These duties made it an important economic point on the river.

The tower's name comes from the Rentenstube, a wood-panelled chamber on the first floor where tolls and harbour dues were collected. Since 26 May 2012 it has been open to the public as part of the Historisches Museum, reached by a historic spiral staircase, with metal floors inside that allow a vertical view through the tower.

The tower has been open to the public since 26 May 2012 as part of the Historisches Museum Frankfurt, reached by a historic spiral staircase. Metal floors inside allow a vertical view through the tower and serve as exhibition space. The Mainufer was raised in the 19th century, so about three metres of the tower's visible height were lost.

The tower lost about three metres of its visible height when the Main embankment was raised in the 19th century. After the First World War the writer Fritz von Unruh lived inside it. Its cellar once held the city prison, which filled with water during Main floods.