The Certosa di San Martino is a former monastery complex and now a museum. Along with Castel Sant'Elmo that stands beside it, this is the most visible landmark of the city, perched atop the Vomero hill that commands the gulf. A Carthusian monastery, it was finished and inaugurated under the rule of Queen Joan I in 1368. It was dedicated to St. Martin of Tours. During the first half of the 16th century it was expanded. Later, in 1623, it was further expanded and became, under the direction of architect Cosimo Fanzago, essentially the structure one sees today.
In the early 19th century, under French rule the monastery was closed and was abandoned by the religious order. Today, the buildings house a museum with a display of Spanish and Bourbon era artifacts, as well as displays of the presepe—Nativity scene—considered to be among the finest in the world.
References:The Basilica of Santa Maria in Trastevere is one of the oldest churches of Rome. The basic floor plan and wall structure of the church date back to the 340s, and much of the structure to 1140-43. The first sanctuary was built in 221 and 227 by Pope Callixtus I and later completed by Pope Julius I.
The inscription on the episcopal throne states that this is the first church in Rome dedicated to Mary, mother of Jesus, although some claim that privilege belongs to the Basilica di Santa Maria Maggiore. A Christian house-church was founded here about 220 by Pope Saint Callixtus I (217-222) on the site of the Taberna meritoria, a refuge for retired soldiers. The area was made available for Christian use by Emperor Alexander Severus when he settled a dispute between the Christians and tavern-keepers.
The church underwent two restorations in the fifth and eighth centuries and in 1140-43 it was re-erected on its old foundations under Pope Innocent II.