In the 17th century, the Spanish heavily fortified the point where the Río Valdivia and the Río Tornagaleones joins the Pacific. Today, the remains of these fortifications at Corral, Niebla and Isla Mancera are a strong reminder of the colonial past.
The largest and most intact is the Castillo de Corral, consisting of the Castillo San Sebastián de la Cruz (1645), the gun emplacements of the Batería de la Argolla (1764) and the Batería de la Cortina (1767).
