Forte Principe da Beira

Built between 1776 and 1783 on the bank of the Guapore River facing Bolivia, this is one of the largest colonial fortifications in Brazil - a square star fort with four bastions, walls of local stone, a moat, and roughly a kilometre of perimeter, put here to make Portuguese possession of the Guapore frontier a physical fact after the Treaty of Madrid redrew the line. It was garrisoned, suffered badly from malaria, and was largely abandoned within decades; photographs from the twentieth century show it swallowed by vegetation. Restoration has cleared and stabilised it, and the scale is the point: an enormous stone work standing in near-empty country hundreds of kilometres from anywhere, with the river running past and Bolivia on the far bank.

What you actually see

• A kilometre of perimeter - four bastions and a moat in cut stone.
• The Guapore frontier - Bolivia directly across the river.
• Scale against emptiness - a major fortification in near-empty country.
• Recovered from forest - cleared and stabilised after decades of abandonment.

When to go

May to September, the dry season. Half a day at the site.

Honest expectations

The drive is the undertaking - Costa Marques is far from any airport and the last road is dirt. There is little interpretation on site and few facilities. Heat is heavy and there is no shade on the walls. Access can close during floods.

Nearby

Costa Marques is the nearest town; Guajara-Mirim is west on the Bolivian border.