An officer in Morocco during his early life, Barreto sailed to Portuguese India and was eventually appointed viceroy of the colony.

Because he had more accurate information on matters in that country, Barreto held back most of this party, although allowing Bishop André de Oviedo to continue with some companions.

[4] According to Robert Kerr in A General History and Collection of Voyages and Travels, Mascarenhas, in a bid to gain a Portuguese ally in the region, had supported a usurper against one Adel Khan, King of Visapur.

Portugal supplied and Barreto commanded a fleet consisting of a galleon and eight caravels alongside Spaniard García de Toledo, and the combined navy took over the island's fort in two days.

After Barreto's return to Portugal, King Sebastian gave him the job of leading an expedition to Monomotapa (Great Zimbabwe) to take over the empire's legendary gold mines.

[7] Barreto set sail from Lisbon on 16 April 1569, with three ships, 2,000 men,[1] and the title of Conqueror of the Mines, bestowed upon him by the king.

[7] The expedition sailed up the Cuama river in November 1571, armed with weapons and mining tools, and arrived in the Sena region on 18 December.

[1] Barreto sent an envoy to the Emperor of Monomotapa with a request for permission to attack a people called the Mongas, whose territory lay between the Portuguese and the mines.

The governor removed him from duty as commander of the São Sebastião fort and returned to Sena where his men were waiting.

[10] Vila-Santa, Nuno, Counter-Reformation Policies versus Geostrategic Politics in the "Estado da India": the case of Governor Francisco Barreto (1555-1558), Journal of Asian History, nº 51 (2017 -2), pp.

[2] Vila-Santa, Nuno, Do Algarve ao Império e à titulação: estratégias de nobilitação na Casa dos Barretos da Quarteira (1383-1599) - Maracanan, nº 19, Jun-Dez.