Castellammare di Stabia is a comune

Comune

In Italy, the comune is the basic administrative division, and may be properly approximated in casual speech by the English word township or municipality.-Importance and function:...

in the province of Naples

Province of Naples

The Province of Naples is a province in the Campania region of Italy. Its capital city is Naples, within the province there are 92 Comuni of the Province of Naples.-Demographics:...

, Campania

Campania

Campania is a region in southern Italy. The region has a population of around 5.8 million people, making it the second-most-populous region of Italy; its total area of 13,590 km² makes it the most densely populated region in the country...

 region, southern Italy

Italy

Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...

. It is situated on the Bay of Naples

Gulf of Naples

The Gulf of Naples is a c. 15 km wide gulf located in the south western coast of Italy, . It opens to the west into the Mediterranean Sea. It is bordered on the north by the cities of Naples and Pozzuoli, on the east by Mount Vesuvius, and on the south by the Sorrentine Peninsula and the main...

 about 30 kilometers southeast of Naples

Naples

Naples is a city in Southern Italy, situated on the country's west coast by the Gulf of Naples. Lying between two notable volcanic regions, Mount Vesuvius and the Phlegraean Fields, it is the capital of the region of Campania and of the province of Naples...

, on the route to Sorrento

Sorrento, Italy

Sorrento is a small town in Campania, southern Italy, with some 16,500 inhabitants. It is a popular tourist destination which can be reached easily from Naples and Pompeii, as it lies at the south-eastern end of the Circumvesuviana rail line...

.
Castellammare di Stabia lies next to the ancient Roman city of Stabiae

Stabiae

Stabiae was an ancient Roman town, located close to the modern town of Castellammare di Stabia approximately 4.5 km southwest of Pompeii. It was positioned on a 50 m high headland overlooking the Gulf of Naples...

, which was destroyed by the Vesuvio eruption in AD 79. The castle the city takes its name from was erected in around the 9th century on a hill commanding the southern side of the Gulf of Naples.