[2][3] When the Treaty of Alcáçovas (1480) confirmed Portugal's monopoly on trade and exploration along Africa's west coast, João II moved quickly to secure and expand his hold on the region.

Diogo Cão filled his ship with stone pillars (padrões) surmounted by the cross of the Order of Christ and engraved with the Portuguese royal arms, planning to erect them at significant landmarks along his voyage of discovery.

[6] In August 1482, Cão arrived at the Congo River mouth and marked it with a padrão erected on Shark Point, commemorating the Portuguese occupation.

He was told that their king lived farther upriver, so he sent four Christian native messengers to search for the ruler and then proceeded south along the coast of present-day Angola where he erected a second padrão, probably marking the termination of this voyage, at Cabo de Santa Maria.

[6] He reached Lisbon by 8 April 1484, where John II ennobled him, promoting him from esquire to a cavalier of his household,[6] and granted him an annuity of ten thousand reals and a coat of arms on which two padrões are depicted.

A legend on the globe created by Martin Behaim reads "hic moritur" (here he dies), seeming to indicate that the explorer lost his life on the coast of Africa in 1486 during his second voyage.

However, sixteenth-century historian João de Barros never mentions Cão's death but wrote instead of his return to the Congo, and subsequent taking of a native envoy back to Portugal.

A coast map by Henricus Martellus Germanus published in 1489 indicated the location of a padrão erected by Diogo Cão in Ponta dos Farilhões nearby Serra Parda, with the legend "et hic moritur" ("and here he died").

[18] Diogo Cão is the subject of Padrão, one of the best-known poems in Fernando Pessoa's book Mensagem, the only one published during the author's lifetime.