The Certosa di San Martino is a former monastery complex, now a museum, in Naples, southern Italy. 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 Joan I of Naples 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.