Cacheu developed near the mouth of its namesake river in the territory of Papel communities, whose rulers controlled land, water, and access to inland networks. Portuguese and Cape Verdean traders known as lançados established themselves in the region during the sixteenth century, intermarrying and relying on African brokers. An English attack in 1567 and disputes with local authorities encouraged traders to seek permission for a fortified post. A first stockade was created around 1588, not through uncontested European occupation but through negotiated and often tense local relationships.

The present stone fort began in 1641 under captain-major Gonçalo Gamboa de Ayala and was completed over several years. Its compact rectangle, corner bastions, thick walls, single gate, and cannon positions protected warehouses, officials, and commerce at the river landing. Water remained a strategic vulnerability, and Papel control of wells could constrain the garrison. The town developed in socially differentiated areas, with Afro-Portuguese and European residents near the river and African communities in surrounding quarters, though trade and family ties crossed those divisions.

Cacheu became a major node in the Atlantic traffic in enslaved Africans. Captives obtained through warfare, raiding, judicial processes, debt, and kidnapping were confined, taxed, and shipped toward Cape Verde, Iberia, and the Americas. Ivory, wax, hides, cloth, and other goods also moved through the port, but human trafficking dominated its historical memory. Chartered companies founded in the late seventeenth century tried to monopolize trade and royal duties, while local merchants, women brokers, African rulers, and smugglers contested company authority.

Power at Cacheu was never simply imposed from Lisbon. Afro-Atlantic families accumulated wealth and influence, and the trader Bibiana Vaz de França famously participated in resistance to company controls. Shifting alliances among Papel authorities, lançados, clergy, captains, and merchants shaped everyday rule. Bissau later surpassed Cacheu as a military and administrative center, especially as Portuguese colonial conquest intensified in the nineteenth and early twentieth centuries. The fort remained a symbol of claims that were for centuries far more limited than colonial maps implied.

After Guinea-Bissau's independence in 1974, the fort survived as a historic structure in a town marked by economic change and war. Restoration in 2004 repaired walls and adapted interior buildings for cultural and community use. Earlier commemorative statues celebrating Portuguese “discoverers” reveal a colonial viewpoint that newer interpretation must contextualize. The nearby Memorial of Slavery and the Slave Trade, opened in 2016, centers trafficking, resistance, and African memory, helping connect the military architecture to the lives harmed by the commerce it protected.

Today the Fortaleza de Cacheu is valued for its architecture and for the difficult history concentrated at the river. Preservation faces tropical rain, vegetation, salt air, limited resources, and the need for locally meaningful use. The fort should not be presented merely as evidence of Portuguese expansion. Its walls record bargaining with African sovereigns, Afro-European communities, female commercial power, corporate rivalry, and the forced movement of thousands of people. Conservation gains purpose when the building supports remembrance, education, and dialogue about the Atlantic world Cacheu helped create.