The Castle of Serravalle, situated on the homonymous hill, dominates the citadel and is visible from any point.
Built by the Marquesses of Malaspina, a family who originatated in the Lunigiana, was erected in the second half of the 12th century.
The original castle, a first fortress, consisted of a few towers in the style of the San Michele castle at Cagliari.
Under the government of the house of Aragon the surrounding walls were extended, several square towers and one pentagonal tower were added to the structure, as well ad an embankment on the seaward side.
In the courtyard of the castle lies the Regnos Altos Church.
It probably was built at the same time ad the main tower (some experts say erlier). At first it was dedicated to St. Andrew but sometime after the year 1847, when a small statue of the Holy Virgin was unearthed in the castles courtyard, the dedication changed to the "Madonna di Regnos Altos", the Queen of the High Kingdom. A doble allusion to the elevate place of the discovery of the statue and the celestial provenience of the subject it personifies.
The Churche building has a rectangular construnction with a semicircular apse and two entrances: one main door on the side of the facade and a lateral door on the North-East side.
In 1972 in the interior a series of important frescoes was discovered. Experts attributed the work to the Tuscanian school and dated its origins in the period of the Judges of Arborea between 1340-1345.
The autors are still unknown, but influence of Franciscans monks seems evident. According to recent interpretations each scene of the frescoes treats one of the Franciscans virtues, as there are castity, charity, humility, courage under torture and the possibility of a good death, a prayer for RIP, a "memento mori".
When observing the painting from the left we can see: the Three Kings Adoration; the Last Supper.
Below: The repentant sinner Magdalena and Saint's theory.
On the wall in front of the apse: Saint Helen with the cross of Christ, S. Christopher, S. George killing the dragon, the Archangel Michel and the Heavenly Women.
On the right wall: a series of Franciscan friars; the Legend of the Three Dead and Three Living People; and finally, St. Lawrence's torture.