Saint Elmo Castle (Castel Sant’Elmo in Italian) is a medieval castle, now a museum, located on the hill of Vomero, Naples next to the Charterhouse of San Martino. It was once called Paturcium and stands in the place where there was, in the tenth century, a church dedicated to St. Erasmus (hence Eramo , Ermo and then Elmo ) .

This imposing building (the first castle for extension of the city), partly derived from the rock (Neapolitan yellow tuff), stems from an observation tower called Norman Belforte .
The first historical records of the castle date back to 132 , when Robert the Wise ordered the regent of the Vicaria, Giovanni de Haya, the construction of a palace, the Palatium castrum, on the hill of St. Erasmus.