Fuerte de Santa Juana de Guadalcazar, Colonial fort in Santa Juana, Chile.

Fuerte de Santa Juana de Guadalcazar is a colonial fort on the southern bank of the Biobio River with hexagonal stone walls and defensive trenches around its perimeter. The structure preserves the design of a typical Spanish military fortification from that era.

The fort was built in 1626 by Governor Luis Fernandez de Cordoba y Arce to protect Spanish territories during conflicts with Mapuche indigenous groups. It represented a key phase of Spanish expansion in southern Chile.

This fortification represents Spanish colonial military architecture and appears on the official shield of Santa Juana municipality. The site shows how Spanish settlers marked their presence in the region through defensive structures.

The fort is located about 600 meters west of Santa Juana's main plaza and is reachable on foot. The surroundings offer views of the river, especially during early morning hours or at sunset.

The fort's hexagonal stone walls are a detail visitors can still pick out. The nearby Rayenantu lagoon fed the moats that surrounded it, and access was by a bridge. The Nahuelbuta range, not the fort, formed the natural barrier that narrowed the route between mountains and river.