Fortress Church, Târgu Mureș, Gothic church building in Târgu Mureș, Romania.

The Fortress Church is the oldest surviving church in Târgu Mureș, built in late Gothic style over roughly a century: a chapel and monastery from 1350–1370, the choir from 1370–1400, and the nave and tower finished by 1450. Its interior was remodelled in 1790 by architect Anton Türk, who added a slightly curved stucco ceiling carried on four pairs of double arches. The 50-metre, four-level tower has broken-arch openings on its top bell level and four small corner turrets around a pointed roof.

Franciscan friars built the church in three campaigns: the chapel and monastery in 1350–1370, the choir in 1370–1400, and the nave and tower by 1450. The sanctuary was consecrated in autumn 1400, the whole church only in 1490. Around 1557–1559 it passed to the Reformed congregation, which removed the Veit Stoss crucifix. In 1658 Turkish troops attacking György Rákóczi II brought down the nave ceiling, destroying the stained glass and the organ; Mihály Teleki funded repairs from 1685 to 1693.

The church was also called the Big Church in the 19th century. Since 1557 it has belonged to the Reformed community, which removed paintings and statues; the Veit Stoss crucifix was taken down and, by oral tradition, thrown into the Nyárád River and later found at Nyárádremete.

The building sits within the historic citadel walls and is easily reached from the central square. Visitors should note that it functions as an active parish church, so opening hours and religious services should be checked before visiting.

A Franciscan seal found in 2010 belonged to a friar sent from another monastery to inspect the local community, a visit made every one or two years and usually entrusted to someone from as far away as possible to keep the report impartial.