Old Arsenal of Mainz Fortress, Military fortress near Mainz Old Town, Germany.

The Old Arsenal (Altes Zeughaus), also called Zum Sautanz, is a three-winged Renaissance building enclosing an open courtyard facing east toward the former Rhine-side city wall. The lower central wing is set back, and a large external spiral staircase with a Welsche Haube canopy stands in the courtyard. Both side wings end toward the city in richly decorated Dutch gables, and Archbishop Bicken's coat of arms appears on the tower's entrance arch.

The Old Arsenal was built in 1604–1605 under Archbishops Johann Adam von Bicken and Johann Schweikhard von Kronberg on the site of an electoral piggery, which gave it the house name Zum Sautanz. From 1738 Johann Maximilian von Welsch built the New Arsenal in baroque forms against its open courtyard side, and the old building served as the electoral mint from 1770. On 27 February 1945 it burned out in the air raid on Mainz and was rebuilt in 1951–52.

The house name Zum Sautanz ("to the dancing pigs") comes from the electoral piggery that stood on this spot before 1604. The building now serves as the seat of the Rhineland-Palatinate state chancellery, and parts of the Landtag administration work here. Visitors can spot Archbishop Johann Adam von Bicken's coat of arms above the entrance arch of the spiral staircase tower.

The building stands inside the old town walls in the northeast of Mainz, near the Hofkanzlei, St. Gangolph and the Martinsburg, with the Kurfürstliches Schloss begun at the same time. The three wings enclose a courtyard open to the east, entered past the spiral staircase tower with its Welsche Haube. The state chancellery and Landtag offices use the building today, so visits are limited to the exterior and the courtyard.

The house name Zum Sautanz ("to the dancing pigs") comes from the electoral piggery that stood on the site before the arsenal was built in 1604–1605. The coat of arms of Archbishop Johann Adam von Bicken can still be seen on the entrance arch of the spiral staircase tower.