The aldobrandesca Rock of Porto Ercole, known more commonly as Rocca Spanish, is a coastal fortification located in the eponymous town of Monte Argentario; It constituted in past centuries one of the bastions of the defensive system of the promontory.

On the hill where now stands the Rocca there was once a small chapel dedicated to St. John the Evangelist, dimensioned by Pope Gregory VII in a 1074 papal bull.