Porto Santo Stefano is a seaport town on the west coast of Italy, in the municipality of Monte Argentario, in the Province of Grosseto, Tuscany. It is the municipal seat of Monte Argentario and one of the two major towns that form the township, along with Porto Ercole. The region is on the slopes of Mount Argentario, which dominates the whole area. Porto Santo Stefano is 150 kilometres (95 miles) northwest of Rome.
Because of the increased exposure to pirate raids, the center had low priority during the rule of Aldobrandeschi and of the Republic of Siena, but with its entry into the State of Presidi in the mid-16th century, the town became a center of great importance in Argentario. It was during this the construction of the Spanish Fort began, a powerful defensive structure that now hosts a permanent exhibition «Submerged Memories». Like all other centers in the area, Porto Santo Stefano joined the Grand Duchy of Tuscany in the first half of the 19th century.
Besides the fortress, the territory still plays host to two Spanish lookout towers; Lividonia and dell'Argentiera, the latter situated on the slopes of Mount Argentario which dominates the whole Santo Stefano area.