The Castle of Mercato San Severino is the second-largest castle in Italy and was founded after 1067 by a Norman knight named Turgisio Sanseverino. The appearance of the castle today has been particularly influenced by the Angevin period. The settlement is marked by three walls: a first nucleus that includes the palatium and the so-called piazza d'armi (army square), and other rooms. The walls of the first enclosure continue south, surrounding a Franciscan convent, the village, and the corresponding church.
The second enclosure with its semicircular towers extends eastward, and it is connected to the last enclosure from the Angevin-Aragonese era, with a triangular perimeter that has a round tower at its vertex. The original size of the site was approximately 350 by 450 meters, with a total area of 157,500 square meters, equivalent to three football fields.
The third enclosure, at a lower elevation, extends eastward with a layout called 'a sperone,' and at its highest point, there is a round tower with three typical Angevin-era gun ports.
The castle was initially owned by the Sanseverino family but was eventually abandoned due to the involvement of one of its members in the Barons' Conspiracy against Ferrante. As a result, Ferrante confiscated the castle from its owners and only returned it after several years, by which time it had lost most of its military characteristics. The castle still partially preserves the chapel and the church. Saint Thomas himself visited this castle to visit his sister, Teodora, who was married to a Sanseverino. The future saint stayed at the Dominican convent. Coins, ceramics, arrowheads, and many other artifacts have been found inside the castle.
The first written record of church in Danmark locality date back to the year 1291. Close to the church are several stones with a Christian text and cross inscribed. The oldest parts of the present red-brick church are from the 1300s. In the late 1400s the church was enlarged to the appearance it has today. The church has been modified both internally and externally several times, among other things after the fires in 1699 and 1889. There are lot of well-preserved mural paintings in the walls.