After 1492 the discovery of the West Indies by Christopher Columbus rendered desirable a delimitation of the Spanish and Portuguese spheres of exploration. This was accomplished by the Treaty of Tordesillas (June 7, 1494), which modified the delimitation authorized by Pope Alexander VI in two bulls issued on May 4, 1493. The treaty gave to Portugal all lands that might be discovered east of a straight line drawn from the Arctic Pole to the Antarctic, at a distance of 370 leagues west of Cape Verde. Spain received the lands discovered west of this line. The known means of measuring longitude were so inexact, however, that the line of demarcation could not in practice be determined (see J. de Andrade Corvo in "Journal das Ciências Matemáticas," xxxi.147–176, Lisbon, 1881), so the treaty was subject to very diverse interpretations. On its provisions were based both the Portuguese claim to Brazil and the Spanish claim to the Moluccas (see History of East Indies). The treaty was chiefly valuable to the Portuguese as a recognition of the prestige they had acquired. That prestige was enormously enhanced when, in 1497–1499, Vasco da Gama completed the voyage to India.