Castel Sant'Elmo is a , now a ; sees its origin in 1275, during the reign of Charles I of Anjou. Between 1538 and 1546 , the castle ( called Sant'Ermo or perhaps from the original St. Elmo St. Erasmus ) found its current configuration . The six-pointed star shape is well suited to the place and function of strategic defensive. Work of rebuilding were carried out in 1599 by Domenico Fontana ( in 1587 lightning struck the ammunition depot , destroying the building of the castle , military housing and the church ) . However, the original structure was never altered by this or subsequent restorations . Theatre of the last acts of the life of the Neapolitan Republic of 1799 ( hosted the last desperate defense of the revolutionaries rebelled against the tyranny of the Bourbons , until their capitulation ), was military property until 1976 , when it began the last restoration , conducted by the Superintendency of Public Works with the intent to return to the city as a center of cultural activity . Inside was made ​​an auditorium that hosts seven hundred people , the ideal venue for large events and public events .