Diego Ramirez de la Diaz first spotted the island in 1470 and named it San Antonio. It was apparently uninhabited until colonized under the Portuguese from 1474, primarily by Africans from Angola via São Tomé Island. These slaves (who the Portuguese called escravos de regate) are considered the first members of Annobonese society. Beginning in the early sixteenth century, many of these slaves who were now marrying Europeans gave birth to the next generations of Annobonese who were called forros (slaves about to be free). Forros began to develop a distinct identity and socio-economic powers. This period also saw the emergence of the Creole Annobonese language. The island was passed to Spain by the 1778 Treaty of El Pardo. The treaty granted Spain control of the Portuguese islands of Annobón and Fernando Po (now Bioko) and the Guinea coast between the Niger and the Ogooué in exchange for Spanish acceptance of the Portuguese occupation of territories in Brazil west of the line established by the Treaty of Tordesillas. The Spanish colony thus formed would eventually be known as Spanish Guinea. The island's populace was opposed to the arrangement and hostile toward the Spaniards. After the handover and when the Spanish flag was hoisted to affirm Spanish sovereignty, the islanders revolted against the newcomers, in part because they were considered heretical for placing dogs on their flag (the actual design represents lions). They expelled them according to a tradition of throwing witches to the sea. A state of anarchy ensued, leading to an arrangement by which the island was administered by a body of five natives, each of whom held the office of governor during the period that elapsed until ten ships landed at the island. This autonomous government continued, with the island claimed by both Spain and Portugal, until the authority of Spain was re-established in the latter part of the 19th century. The island briefly became part of the Elobey, Annobón and Corisco colony until 1909. The British erected a fort at "St Antony" in 1801, eventually legalized through a lease from the Spanish government in 1827. The base was used by the British to suppress the Atlantic slave trade. During the final years of the administration of Francisco Macías Nguema, the first president of Equatorial Guinea, the island was called Pigalu or Pagalu. The population felt prejudice against them in Equatorial Guinea and some began advocating separatist movements.