Together with the adjacent Certosa di San Martino, this forms an important
group of buildings situated on the hill on which the quarter of Vomero has grown up.
Castel Sant'Elmo was also built on the orders of Charles of Anjou: its construction, in tuff, was begun in 1329 and completed in 1343 by the work of the architects Tino da Camaino, Atanasio Primario and Francesco di Vito.
The building, whose architectural features from a distance resemble those of the Castel dell'Ovo, was one of the city's fortifications and was used above all to protect it from invasions from the sea.
It was built where the Normans, in 1170, had a fort called Belforte surrounded by rich vegetation.
All Naples' historic events involve Castel Sant'Elmo.
The King Charles V, through the viceroy Pedro de Toledo, rebuilt completely the castle by the work of the Spanish architect Pier Luigi Scribā, that designed the star-shaped plan of the castle.
It has witnessed numerous sieges, fierce disputes between the various dominating powers, and repeated popular uprisings, including the now legendary Masaniello revolt of 1647.
The old fort has risked destruction several times.
During the Second World War the Germans had intended to blow it up before they left the city, changing their minds only at the last minute.
The castle, which has now been restored, having been freed from its use as a military prison, houses exhibitions of art and history and also contains the Molaioli Library of Art and a videotheque which supplies information on all of the city's monuments.
The complex also contains the 16th century Church of Sant'Elmo and the Chapel of Santa Maria del Pilar (17th century).
From the communication trenches and the Castle's upper square there is an extensive view over the city and Vesuvius, the Neapolitan plain, and the marvellous gulf bounded by Capri and the profile of the Phlegraen islands.
It is worthy to visit the Church of St. Erasmo that has a rich floor in maiolica and tile. Behind the altar there is the tomb of Pietro de Toledo, a viceroy's relative and first lord of St. Elmo.
In front of the entrance of the church there are the prisons where were imprisoned, among many others : the Princess Giovanna di Capua, Tommaso Campanella, Angelo Carasale the architect of the San Carlo theatre and many revolutionaries: Mario Pagano, Domenico Cirillo, Gennaro Sessa di Cassano, Francesco Pignatelli, the Count Ettore Carafa, Luigia Sanfelice, Pietro Colletta, Carlo Poerio, Silvio Spaventa and many others.