Fuerte San Carlos, Military fortification in Corral, Chile.

Fuerte San Carlos stands at the western end of the southern shore of Corral Bay, part of the Valdivia fort system. Begun in 1762 to plans by José Antonio Birt, it was a parapeted enclosure for the troops, joined by a drawbridge to a battery of six 24-pounder cannons with a furnace for heating shot. Only the ruins of its walls remain today.

The fortification was built in the 1700s to protect Spanish colonial trade and the coast from pirates, privateers, and enemy naval forces. It became one of several defense systems constructed along this coast to secure Spanish colonial interests in the region.

The structure reflects Spanish engineering practices from the colonial era, showing how military designs adapted European defensive concepts to this South American coast. Local residents and visitors can see these methods preserved in the remaining stonework and earthworks.

The site is easily reached from Corral and can be explored on foot, with the ruins scattered across the coastal grounds. Wear sturdy shoes since the terrain is uneven and some sections are overgrown with vegetation.

Before the fort was built, Corral Island was artificially lowered and joined to the mainland, turning it into the peninsula where San Carlos stands. The site was declared a National Monument by Supreme Decree 3869 of 1950. Since 2015 the structures have deteriorated from abandonment, and historical re-enactments by Corral's tourism office take place only at Fuerte San Sebastián.