Fort Bellecroix, 18th-century military fortification in Metz, France.

Fort Bellecroix is an 18th-century military structure in Metz with four large bastions and several defensive walls surrounded by deep dry moats. Underground passages run throughout the construction and allow exploration beneath the surface.

Vauban had noted the site, a few hundred metres from the centre, was poorly defended; after the 1697 Treaty of Ryswick returned Luxembourg to the Spanish Netherlands, Marshal Belle-Isle pressed the king to strengthen Metz. Louis de Cormontaigne designed a double crown to cover the lower Seille front, paired with Fort Moselle on the Moselle side. Expropriations ran from 1731 to 1735, building began in 1734 and ended in 1740.

The name Bellecroix comes from a calvary and chapel razed in 1731 to clear the site. The fort was built as the counterpart of Fort Moselle: Cormontaigne's double crown guarded the lower Seille front while Fort Moselle covered the Moselle side. After decommissioning in April 1954, the grounds passed to the state and over 80 hectares were opened to housing, with a large public rental estate built inside the fort and on its glacis.

The fort lies a few hundred metres from Metz city centre, and its three former military servitude zones were lifted so that over 80 hectares opened to urban development. The Steinmetz barracks was added along boulevard de Trêves. Expect a bastioned enclosure of four bastions, three curtain walls, three demi-lunes and a lunette, ringed by 3 km of dry moats.

After the fort was decommissioned in April 1954 and transferred to state private domain, the removal of three military servitude zones opened more than 80 hectares to urbanisation. Public rental housing of the grand ensemble type was built inside the fort and on its glacis.