The casting hall in the Gothic style at the Bendorf ironworks, Sayn, 10 km north of Koblenz, is one of the most monumental industrial buildings in Europe. A blast furnaces was built at Bendorf in 1769 by Clemens Wenzeslaus, Elector of Trier. When the state of Nassau was absorbed into Prussia the ironworks fell under the control of the Prussian government, and under the direction of a Prussian civil servant, Karl Ludwig Althans (1788-1864) a new blast furnace was constructed in 1821.
In 1828 work began on the casting hall, a triple-naved basilica of six bays, 24 m long and 29 m wide, fabricated from hollow cast-iron pillars and arches, all made at the works. The hall was extended with four further bays in 1844. The front of the hall is glazed, with cast-iron ribs arranged in pointed arches. Several pillar cranes with ball-bearing mechanisms designed by Althans are preserved n the hall. The designs of Prussian state buildings were supervised by a committee in Berlin, and it is likely that Karl Friedrich Schinkel influenced the decision to build the casting hall in the Gothic style rather than in the ponderous Grecian manner originally proposed by Althans.
The Sayn ironworks cast cannon for the fortresses at Koblenz and Ehrenbreitstein, but then came to specialise in ornamental castings, a collection of which is displayed in the Rheinisches Eisenkunstgussmuseum at nearby Schloss Sayn, historic home of the princes of Sayn-Wittgenstein.
In 1866 the ironworks passed into the control of the Krupp company, which blew out the blast furnace in 1878, and closed the concern completely in 1926, when the buildings passed to the local municipality. A private firm bought them in 1976 and has been responsible for their restoration.