The Spanish Crown saw early the strategic nature of the southern region of Chile, through the Strait of Magellan and Cape Horn was halfway point for navigation from Europe to the American Pacific coast. From the late sixteenth century, the construction of fortifications in this area became a high priority, because of the frequent traffic of ships French, English and Netherlands, in particular due to the incursions of the pirates. The destruction wrought on the coast of Chile and Peru by Francis Drake in 1578, joined the expedition as Hendrik Brouwer, who temporarily occupied in 1643 adjoining the coast at the mouth of Valdivia River. This led to the peninsular authorities to undertake the construction of powerful defensive fortifications in Valdivia, and Chiloe Valparaiso.
In 1645 the Viceroy of Peru, the Marquis of Mancera, began implementing the plan, sending a huge armada to refound the city of Valdivia-devastated following the Indian uprising of 1598 - and building fortifications on the coast. Highlight including Castello San Luis de Alba, located on the tip called bitters, near the mouth of the river Valdivia. It was built entirely of stone. It was felt that their equipment and structure could compete "with the most celebrated of Europe."
Fort San Luis de Alba had eleven pieces of artillery, which by its studied location could beat the anchorage of the enemy ships. Was isolated from the outside world by a moat, which is crossed by a drawbridge. Inside were, in addition to the barracks and the Commandant s house, a chapel. In the late eighteenth century, the fortress was strengthened and joined him a few brick buildings. Currently, none of the buildings inside the complex stands, but the basic structure with their artillery remains and has undergone restoration.
El Castillo San Luis de Alba of bitters, along with the rest of the fortifications of Valdivia, constituted the largest defense complex of the American Pacific coast.