In 1494, Spain and Portugal signed the Treaty of Tordesillas, which drew an imaginary line through the Atlantic Ocean. With the Pope's blessing, they agreed that all newly discovered lands to the west of the line belonged to Spain, while everything to the east belonged to Portugal.
The Atlantic Rivalry Before 1494
In the late fifteenth century, the maritime kingdoms of Portugal and Castile were locked in fierce competition over Atlantic navigation and trade routes. Throughout the 1400s, Portuguese mariners under the patronage of figures like Prince Henry the Navigator methodically charted the western coast of Africa, seeking a direct sea route to the valuable spice markets of Asia. These efforts were formalized in previous agreements, most notably the 1479 Treaty of Alcáçovas, which granted Portugal exclusive rights to navigate, trade, and conquer south of the Canary Islands, while Castile retained the Canaries themselves.
This balance of power collapsed in March 1493 when Christopher Columbus returned from his voyage across the Atlantic. Sailing under the banner of the Catholic Monarchs of Spain, Ferdinand II of Aragon and Isabella I of Castile, Columbus claimed to have reached the Asian continent by sailing west. King John II of Portugal immediately asserted that the newly discovered islands fell within the Portuguese sphere established by Alcáçovas, given their latitude south of the Canaries. Ferdinand and Isabella rejected this interpretation, arguing that Columbus had explored uncharted oceanic waters directly to the west, setting off an urgent diplomatic struggle.
The Papal Bulls and the First Boundary
To consolidate their claims, the Spanish monarchs turned to Pope Alexander VI, a native of Valencia in the Crown of Aragon. In 1493, the Pope issued a series of papal bulls, the most influential of which was Inter caetera. The decree granted Castile title to all lands discovered, or yet to be discovered, west and south of a meridian drawn 100 leagues west and south of the Azores and Cape Verde islands, provided those lands were not already held by a Christian prince.
The 100-league line favored Spain heavily and posed an immediate threat to Portuguese maritime strategy. To navigate around the southern tip of Africa, Portuguese ships relied on a navigational maneuver known as the volta do mar, swinging far out into the open Atlantic to catch favorable winds and avoid unfavorable coastal currents. A boundary line set merely 100 leagues west of Cape Verde would severely constrain Portuguese fleets, potentially forcing them into waters claimed exclusively by the Spanish crown.
The Treaty of Tordesillas
Recognizing that the papal decree was unworkable and risked armed conflict, King John II initiated direct bilateral negotiations with Ferdinand and Isabella. Diplomats from both kingdoms met in the Castilian town of Tordesillas in early 1494. Rather than rely solely on papal authority, the two powers negotiated a binding political treaty signed on June 7, 1494, which Pope Julius II later ratified with the bull Ea quae pro bono pacis in 1506.
The central compromise of the Treaty of Tordesillas was the relocation of the demarcation line. The envoys agreed to move the meridian to 370 leagues west of the Cape Verde islands. Under this arrangement, all lands and islands discovered to the west of the meridian belonged to Castile, while all territories to the east of the line, including the sea route around Africa to India, belonged to Portugal. Spanish ships were permitted passage through Portuguese waters to reach their western territories, but they were forbidden from trading or settling in Portuguese zones.
Brazil and the Shifting Global Map
At the time the treaty was signed, neither party possessed an accurate map of the Atlantic basin or understood the true continental scale of the landmasses Columbus had encountered. The renegotiation to 370 leagues was primarily intended by Portugal to secure open-ocean navigation for its African voyages. However, this westward shift had massive, unexpected territorial consequences in the Americas.
In 1500, a Portuguese fleet commanded by Pedro Álvares Cabral sailed far to the southwest to catch Atlantic trade winds on its way to India and made landfall on the eastern coast of South America. Because the coastline of modern-day Brazil projected eastward across the 370-league meridian, Portugal laid claim to the territory under the terms of the 1494 treaty. This single diplomatic adjustment ensured that South America would ultimately be divided between Portuguese and Spanish cultural and linguistic domains.
The Anti-Meridian and the Treaty of Zaragoza
The Treaty of Tordesillas successfully established a division in the Atlantic Ocean, but it did not explicitly define how the line continued on the opposite side of the globe. As knowledge of global geography expanded, particularly following Ferdinand Magellan's expedition from 1519 to 1522 which circumnavigated the Earth under the Spanish flag, the two empires clashed over territorial rights in the Asia-Pacific region.
The primary flashpoint was the Moluccas, or the Spice Islands, in modern Indonesia. Both empires claimed that the lucrative archipelago fell within their hemisphere on the other side of the world. Because determining longitude at sea was technically impossible with sixteenth-century instruments, neither side could definitively prove where the anti-meridian lay. The conflict was finally resolved in 1529 with the Treaty of Zaragoza, in which Spain surrendered its claim to the Moluccas in exchange for a substantial cash payment from Portugal, establishing a secondary boundary line in the Pacific.
Enforcement, Ambiguity, and European Backlash
Implementing the Treaty of Tordesillas was plagued by technical and practical challenges. The treaty text never specified which exact island in the Cape Verde archipelago the 370 leagues should be measured from, nor did it define the precise length of a marine league. Because measuring longitude accurately at sea was not solved until the development of reliable marine chronometers in the eighteenth century, maps drawn by Spanish and Portuguese cartographers routinely placed the boundary line wherever it best suited their national interests.
Furthermore, other European maritime nations entirely rejected the idea that two kingdoms and the Pope could divide the globe between themselves. Monarchs such as Francis I of France and later Protestant rulers in England and the Netherlands refused to recognize the treaty. Francis I famously demanded to see the clause in Adam's will that excluded him from sharing in the world's wealth. In the seventeenth and eighteenth centuries, English, Dutch, and French privateers, traders, and colonists established their own settlements across the Americas and Asia, ultimately dismantling the Iberian monopoly.
Key takeaways
•The Treaty of Tordesillas (1494) established a north-south meridian 370 leagues west of Cape Verde, giving Spain rights to lands to the west and Portugal rights to lands to the east.
•Moving the line 370 leagues west of Cape Verde was intended to protect Portuguese sailing routes around Africa, but unintentionally gave Portugal legal claim to Brazil after its 1500 discovery.
•Because the treaty only drew a line in the Atlantic, the two crowns had to sign the Treaty of Zaragoza in 1529 to create an anti-meridian dividing the Pacific and the Asian spice trade.
•The treaty could not be measured precisely due to sixteenth-century navigational limits, and competing European powers like France, England, and the Netherlands refused to recognize its authority.