Protected from direct Spanish competition by the treaty of Tordesillas, Portuguese eastward exploration and colonization continued apace. Twice, in 1485 and 1488, Portugal officially rejected Christopher Columbus's idea of reaching India by sailing westwards. King John II of Portugal's experts rejected it, for they held the opinion that Columbus's estimation of a travel distance of was undervalued, and in part because Bartolomeu Dias departed in 1487 trying the rounding of the southern tip of Africa, therefore they believed that sailing east would require a far shorter journey. Dias's return from the Cape of Good Hope in 1488, and Pêro da Covilhã's travel to Ethiopia overland indicated that the richness of the Indian Sea was accessible from the Atlantic. A long-overdue expedition was prepared.