Martinikirche, Gothic church in Siegen, Germany.

The Martinikirche is a Gothic church in Siegen built on a western promontory of the city and featuring pointed arches, ribbed vaults, and carefully fitted stonework. The interior displays typical medieval church structure with soaring ceilings and decorative stone elements throughout the sanctuary.

The Martinikirche was first documented on 3 June 1311, when a charter assigned it income from the "Mashütte uf der Weste" smelting works on the Weiß and from gardens outside the Marburger Tor. Archaeology points to a Frankish-Carolingian predecessor, probably a fortress chapel of around the mid-8th century; a 10th-century floor mosaic found under the north aisle belonged to that earlier sacred building. In the 16th century the church lost its role as Siegen's parish church to the Nikolaikirche, and after the Unteres Schloss was built in the 17th century it was used only for funerals before falling into decay. Restored from 1833 to 1838 after a merchant's donation, it was rebuilt to 1949 following destruction in the Second World War.

The church is dedicated to St Martin and has been Protestant since the Reformation. Its name recalls the medieval Kölner Straße and Kölner Tor, the western gate of Siegen beside which it stands. In the 18th century it was used only for funerals and burial services.

The church stands on the western rocky spur of the Siegberg, immediately west of Siegen's Lower Castle, at the edge of the medieval town core. The site is reached on foot via the old upper town; the street names Kölner Straße and Marburger Straße recall the historic road across the Sieg. The floor of the church lies above the excavated 10th-century mosaic, which rests 92 cm below the present surface.

Archaeological excavations beneath the church floor uncovered a 10th-century floor mosaic that remains in place. This discovery reveals that the site held religious significance and continuous use for many centuries before the current building was erected.