The small castle of Saint Carlos has been protecting the port of Palma for five centuries. In 1600, it was ordered to be built to protect sea routes by King Philip III of Spain. Construction, whose funding was divided between the budget of the monarchy and the college of commerce, began in 1610 and ended in 1612. Initially, the fort was named Porto Pi Castle, but soon got its current name in honor of the Viceroy of Mallorca, Carlos Coloma. In 1662-63, the castle, rectangular in plan, containing only 5-6 cannons at that time, was expanded with the participation of engineer Vicente Muta. In addition, during the War of Spanish Succession, it was additionally fortified from the sea. At the end of the 19th century, the castle was repaired, technically equipped, a dam was dug on the western side.

The castle is well preserved, it is illuminated at night. During the Civil War, the fort served as a prison for political prisoners. Currently, it houses the naval base of Porto Pi, as well as the Museum of the military history of the city, which has a large collection of weapons, maps, uniforms, archival documents. The castle is a national treasure of Spain.