Château fort de Nesle, Medieval fortress in Nesle-et-Massoult, France.

The Château fort de Nesle stands on a rocky spur above a hairpin bend of the RD 19 in Nesle-et-Massoult. Only a still-inhabited corps de logis remains, with two mullioned windows and a guardroom grille; a curtain wall with a walkway links it to the donjon base. To the west survive a chimney corbel and the base of an octagonal stair turret.

The primitive castle dates from the 13th century, as shown by its cartulary, a 117-folio parchment volume with 83 acts written between 1217 and 1282, kept at the Musée Condé in Chantilly. In 1418 Jacques de Courtiamble asked Duke John the Fearless to enlarge his fief of Nesle. In 1512 the castle passed to Guillaume de Montmorency, and by 1695 it had two square towers of four to five storeys and a walled courtyard.

The castle's 13th-century cartulary, a 117-folio parchment volume recording 83 acts from 1217 to 1282 in Latin and Middle French, is kept at the Musée Condé in Chantilly, later bound by the duc d'Aumale. It was the subject of a paper at the Thouars colloquium of 8–10 June 2006 on Jean, seigneur de Nesle.

The ruins are privately owned and not open to the public, so viewing is limited to external perspectives from surrounding paths and roads. Photography of the structure from outside is possible if you visit the surrounding area.

The octagonal element at the west end of the terrace is not a full tower but the base of a staircase turret, recorded alongside a surviving chimney corbel. The castle's 13th-century cartulary, 83 acts on 117 parchment folios, is kept at the Musée Condé in Chantilly.