The political and cosmographical background to the Spanish incursion into the Pacific in the sixteenth century
Colin Jack-Hinton’s 1964 article examines how the interlocking problems of Iberian diplomatic rivalry and classical cosmographical uncertainty shaped the Spanish claim to the Pacific and the Moluccas in the sixteenth century. His central thesis is that the Spanish delineation of the antipodal demarcation line some 30° west of its true position was not an act of deliberate cartographical fraud but an honest consequence of the Ptolemaic degree value and the inability to determine longitude with any precision.
Summary
Jack-Hinton traces the diplomatic framework from the Canarian disputes of the fourteenth century through the Papal Bulls of 1493, the Treaty of Tordesillas (1494), and the Treaty of Saragossa (1529), arguing that the Papacy functioned as a mediator seeking to maintain peace between the two Catholic maritime powers rather than as an authority wielding dogmatic or proprietary power. The Bulls were consistently revocable and framed as limitations on each nation’s sphere of exploration rather than as donations of territory, a reading supported by the Papacy’s failure to censure English, French, and other Catholic ventures into the same waters (pp. 130–131).
The article’s substantive core addresses the cosmographical confusion that made the position of the antipodal demarcation indeterminate. Spain and Portugal had inherited different classical concepts of the earth’s circumference: the Ptolemaic 180,000 stadia (yielding a degree of 16⅔ leagues of 3 Roman miles, or 50 nautical miles) and the Eratosthenian 252,000 stadia (yielding 17½ leagues of 4 Roman miles, or 56 nautical miles). These differences meant that even when both parties agreed on the league value, they would disagree by 150 leagues on the position of the antipodal line, with the Moluccas falling on opposite sides of it depending on which concept was applied (pp. 133–134, 142–143). Jack-Hinton demonstrates through a wide range of contemporary sources—Encisco’s Suma de Geographia, the deliberations of the Junta of Badajoz, Pigafetta’s navigational notes, and the charts of Ribero, Velasco, and Herrera—that the Ptolemaic concept persisted in Spanish usage well into the century, and that the Spanish claim to the Moluccas was a rational (if erroneous) deduction from that framework rather than a calculated deception (pp. 135–136, 147–149, 153–154).
The article also addresses the question of whether Magellan’s expedition deliberately falsified its Pacific crossing distances. Jack-Hinton sides with Wallis in rejecting the falsification theory, attributing the underestimates to the inherent limitations of dead-reckoning navigation, the difficulty of accounting for westerly currents, and Magellan’s honest expectation that the Pacific would be narrower than it proved to be (pp. 144–145).
Key Findings
- The Treaty of Tordesillas (June 1494) fixed the Atlantic demarcation at 370 leagues west of the Cape Verde Islands; the Treaty of Saragossa (April 17, 1529) pledged Spain’s claim to the Moluccas for 350,000 ducats and fixed the antipodal demarcation at 17° east of the Moluccas, defined as 297½ leagues (pp. 129, 149).
- The Ptolemaic degree of 16⅔ leagues (50 nautical miles) gave a hemispherical extent of 3,000 leagues; the Eratosthenian degree of 17½ leagues (56 nautical miles) gave 3,150 leagues—a difference of 150 leagues that determined whether the Moluccas fell in the Spanish or Portuguese hemisphere (pp. 142–143).
- Encisco’s Suma de Geographia (1519) argued the world’s circumference was 6,000 leagues and that only 230 leagues remained in the Portuguese hemisphere beyond Malacca, placing the Moluccas firmly in the Spanish sphere (p. 135).
- At the Junta of Badajoz (1524), the Spanish cosmographers accepted the degree of 17½ leagues “used commonly by sailors both in Portugal and Castille” but simultaneously adhered to Ptolemy’s circumference of 62½ miles per degree, revealing the internal inconsistency of their position (p. 147).
- Diego Ribero’s World-Map of 1529 depicted the Pacific as 134° of longitude wide from Central America to the Moluccas—an underestimate of approximately 15° but a unique approximation to accuracy that was not matched by his immediate successors, who continued to show a narrow Pacific until the turn of the seventeenth century (p. 151).
- The degree of 17½ leagues (70 Roman miles) underestimated the true equatorial circumference by 1,440 nautical miles or 24°, a margin that both generated and concealed the Spanish underestimate of the Pacific’s width (p. 156).
Conclusion
Jack-Hinton concludes that the Spanish incursion into the Pacific was undertaken against a background of cosmographical concepts that simultaneously constrained navigational expectations and provided a seemingly irrefutable legal basis for Spanish dominion over the ocean and its contents. The persistent Spanish cartographical depiction of the antipodal demarcation west of Malacca, continuing into the early seventeenth century, was an honest consequence of an underestimated Pacific width rather than a deliberate falsification, and it was only the emergence of accurate Dutch cartography and the accumulation of multiple Spanish Pacific voyages that finally corrected the error (pp. 153–156).
Context
- The article draws on archival material from the Archivo General de Simancas (Estado, legajo 219) and the Biblioteca Nacional, Madrid (MS 3099), as well as the John Carter Brown Library holdings of Velasco’s Demarcacion y Division de las Indias (c. 1575).
- Historiographically, the article engages with and corrects the work of Nunn (1936) on Magellan’s route, Wallis (1954) on Pacific exploration, and the earlier metrological studies of Dawson (1899) and Bourne (1891), while also identifying and correcting a persistent error in Burney’s (1803) treatment of the Iberian league value that had been propagated by Guppy and Sharp.