The name of the settlement comes from the slave "kal" or "kalinik (= clay, clayey). The Saxon name of the locality is Kelling and is coming from the early masters, the nobles Kelling. They were greavi of Câlnic (Saxon: Graeve or Gräve, German: Graf, Hungarian: Grof - meaning great landlord or earl) and they are mentioned from 1267, 1269 and 1309. One of them, Chyl de Kelling, built in the middle of the 13th century the dungeon of Câlnic and used it as housing. Chyl then bought Blaj and his followers have continued to buy the villages of Cut, Vingard and many other territories. At Câlnic was found prehistoric material, and vague medieval traces from the 11-12th centuries, but the medieval settlement itself dates from the 12-13th centuries. The most consistent area is corresponding to the consolidation of power of the Saxon earls (1267).
The first residence contained a quadrilateral hall (probably an initial dungeon or a rectangular altar of the Chapel). The dungeon was built around 1272 and has a rectangular shape. It was called the Siegfried Tower, and the thickness of the walls reach one meter. Initially was only 14 m high, but was subsequently raised to 20 m. At the ground floor was a cellar with a semi-cylinder dome, same for the first floor, but the other levels have no dome, but a ceiling. On the first floor there is a fireplace, and were founded fragments of enameled tiles. During the 1962-1964 restoration was discovered a clover-shaped bipartite window, indicating an early Gothic phase, perhaps in the second half of 13th century.
The fortress has been designed with a inhabited massive rectangular keep protected by an oval precinct, fortified with defense tower to the south, a rectangular gate tower to the northwest and probably filled by a drawbridge; it was probably a ditch 3 m deep and 10 m wide. Subsequently was built the chapel, dated by coins from the time of kings Bela IV and Stefan V. Restoration work and pickling have revealed the existence of three rectangular windows slightly arched at the top on the west wall and one on the southern wall. The two Gothic windows, visible today, were built later and dates from the mid-14th century. The triumphal arch store the remains of two successive murals, the latest being a bust of Christ.
The last descendant of the noble family sold the fortress to the Saxon peasant community of Câlnic. Beginning with the first half of the 14th century, the community started to erect a new wall, to fortify the gate-tower by a barbican and to build a chapel in the courtyard, on the ruins of the former construction. One can find fragments of a fresco from the beginning of the 16th century, a wooden stand on the west side from 1733, decorated with panels painted in the floral Renaissance style, inspired from folk art. Provision larders have been built in the courtyard, along the walls, to be used in times of affliction. The raising of the second precinct in the 15th century was followed by the ranging in tiers of the keep by two floors, reaching a height of more than 20 meters, ensuring thus an efficiency of the fire arms beyond the exterior wall.
The fortress was restored between 1962-1964 by the Romanian Board for Historical Monuments, and today has been transformed into an international scientific and cultural center.