Château de Berzy-le-Sec, Medieval castle in Berzy-le-Sec, France.

Château de Berzy-le-Sec is a castle with a square layout and corner towers surrounding a central courtyard. The buildings around the yard show traces of former living spaces and storage areas that once served the residents.

The castle dates from the 14th or 15th century and was remodelled in the 16th century. Around 1445 the lordship was acquired by Pierre de Louvain, who had the castle rebuilt or altered. It remained inhabited until 1918, when bombardments caused severe damage, and its remains were classified as a monument historique by decree of 13 July 1926.

The protruding chapel by the entrance has 16th-century rib vaulting and was built in carefully fitted limestone courses; its wide windows facing the ditch gave the entrance symbolic protection. A stone medallion with a coat of arms from the castle is now set into a wall of the former abbey church of Saint-Léger, which houses the Soissons museum.

The ruins stand beside the Romanesque church of Berzy-le-Sec, in the delegated commune within Bernoy-le-Château, Aisne. The site is a classified monument with no visitor facilities, and the remains are open, uneven masonry, so access is not arranged for the public. The eastern building survives best; the north side has nothing left, and a long metal shed now occupies the former outer bailey on the plateau side.

A stone medallion carved with coats of arms, taken from the castle, is set into a wall of the former abbey church of Saint-Léger, now the Musée de Soissons. Its shield is split: three paired bars on one side, the other side worn and illegible.