Castle of Pianisi, Medieval castle in Sant'Elia a Pianisi, Italy.

The Castle of Pianisi is a ruined medieval castle on a hill about 3.7 km northwest of Sant'Elia a Pianisi, near the Fortore river. Excavations in 2013–2015 uncovered stretches of the upper terrace walls, a large cylindrical tower and the remains of the church of Santa Maria in Planisi, built with regular rough-hewn limestone blocks.

The name Pianisi first appears in a diploma of Pope Paschal I (817–824), confirmed by later popes and emperors Otto I, Otto II, Henry II and Conrad II. The castle is documented from June 1008, though that charter is a forgery no earlier than the late 12th century. In 1269 it belonged to Jean de Nanteuil and was valued at 30 gold ounces; in 1276 Charles I of Anjou granted it to Tipaldus Alamannus. Some sources say the 1306 earthquake destroyed it.

The site's name comes from the Pianisi toponym, first recorded in a 9th-century papal diploma confirming the church of Santa Maria in Planisi to the Abbey of San Vincenzo al Volturno. The castle's church of San Pietro preserves a late 14th-century fresco of a knight fighting a winged dragon, identified as Jean de Nanteuil, lord of Pianisi in 1269. The church was deconsecrated in 1701 by Archbishop Vincenzo Maria Orsini, later Pope Benedict XIII; its baptismal font now stands in a public fountain in Sant'Elia a Pianisi.

Visitors can reach the castle ruins by following signs from the central square of Sant'Elia a Pianisi. Parking is available nearby, and the location is accessible from several walking trails in the area.

Excavations by the University of Molise between 2013 and 2015 uncovered the large cylindrical tower that once overlooked the settlement, along with the remains of the church of Santa Maria "in Planisi". Its great apse and sturdy bell tower were built from very regular ashlar blocks split along the natural fissures of the local limestone.