Pfaffenturm, Medieval fortified tower in Aachen, Germany.

The Pfaffenturm is a medieval fortified tower in Aachen with a circular floor plan measuring roughly 9 meters across. The structure rises over two stories to about 8.65 meters high, with several windows that replaced the original arrow slits and shooting holes.

The tower was built between 1442 and 1456 as part of Aachen's outer defensive walls. It was positioned between Junkerstor and Königstor gateways near the Johannisbach stream and served the city's medieval defense system.

The name Pfaffenturm comes from the clerics of the Münsterstift, who had to pay and feed the guard crew of this tower. The tower also carried the name Suylisturm, after the Johannisbach stream (Suylisbach) that flowed just south of it under the wall. Today the student association K.D.St.V. Ripuaria Aachen uses the tower.

The tower stands at the corner of Lochnerstraße and Junkerstraße, a short walk from the Junkerstor and Königstor sites. It is a built structure in a residential street, so the exterior is seen from the pavement; the interior is used by the student association K.D.St.V. Ripuaria Aachen and is not open as a regular visitor attraction.

The tower's circular plan and its arrow slits facing inward toward the city show it also served as a refuge for citizens if attackers had already breached the walls. The Johannisbach stream, also called Suylisbach, flowed directly beneath the tower and fed the moat; its opening was protected by a heavy iron grate.