Forte de São Gabriel da Cachoeira, Military fortress in São Gabriel da Cachoeira, Brazil.

Forte de São Gabriel da Cachoeira is a military fortress located on Fortaleza Hill along the left bank of the Rio Negro River, positioned to control traffic along the waterway. Its surviving foundation remains and historical artillery pieces are displayed in public spaces throughout the town.

German military engineer Philipp Sturm selected this strategic hilltop location and began construction in January 1763 as part of Portuguese colonial expansion. The fortress became a key post in defending Portuguese territory against Spanish claims in the Amazon region.

The fort gave its name to the settlement that became São Gabriel da Cachoeira, elevated to vila in 1833 in honour of governor Gabriel de Souza Filgueiras. The site is also linked to the Carmelite missions that, from 1695, crossed the rapids to catechise the indigenous peoples of the Uaupés, Tiquié and Içana rivers.

The fort stood on the left bank of the upper Rio Negro at the morro da Fortaleza, in what is now the town of São Gabriel da Cachoeira. The site is reached by river or by air to the town's airport; no road connects it to Manaus. The original structure no longer stands, so look for the hill itself and the town that grew around it.

The fortress was designed and built by a German military engineer rather than a Portuguese one, reflecting how colonial powers hired specialized expertise from across Europe. Today it stands in one of Brazil's largest municipalities by area, a region where five indigenous languages now hold official status.