First Treaty of San Ildefonso (October 1, 1777). Preliminary treaty on the territorial limits of Spain and Portugal in South America. The Portuguese crown ceded to Spain the southern half of present-day Uruguay, including Colonia del Sacramento. Also the islands of Annobón and Fernando Poo in Guinean waters. The Spanish Crown accepted the withdrawal of the Santa Catarina Island, on the Brazilian coast. Agreed and concluded by King Charles III of Spain and Queen Maria I of Portugal. Ratified by the King at San Lorenzo de El Escorial on 11 October of that year. Collection of the Treaties of Peace, Alliance, Commerce adjusted by the Crown of Spain with the Foreign Powers (Colección de los Tratados de Paz, Alianza, Comercio ajustados por la Corona de España con las Potencias Extranjeras). Volume III. Madrid, 1801. Historical Military Library of Barcelona, Catalonia, Spain.