Why did the Portuguese establish trading posts at Sena and Tete on the Zambezi River?

In the 1530s, the Portuguese established trading posts and garrisons at Sena and Tete along the Zambezi River primarily to secure exclusive control over the regional gold trade.12

By pushing into the interior, the Portuguese sought to bypass existing trade networks and discover precious mineral sources for themselves, following routes previously utilized by Muslim traders. These outposts served as centers where local populations exchanged gold and ivory for European goods like beads and cloth. To further consolidate their influence and legitimize their presence, the Portuguese utilized these locations as bases for the prazo system, which involved land grants that allowed them to extract tribute from local populations and exert greater authority in the region.3412