Some documents merely describe the world; others dare to divide it. The Treaty of Tordesillas, signed on 7 June 1494 in the Castilian town that gave it its name, belongs firmly to the second category. With the ink barely dry, Castile and Portugal parcelled out on paper lands no European had set foot on, oceans no one had charted and peoples whose very existence was unsuspected. Rarely have a handful of clauses had such far-reaching consequences.
From a papal bull to a pact
The starting point was not Tordesillas but Rome. After Columbus returned, the Catholic Monarchs sought legal cover for their discoveries and found it in Pope Alexander VI, a Valencian by birth, who issued several bulls in 1493. The most famous, Inter caetera, drew a pole-to-pole line one hundred leagues west of the Azores and Cape Verde: whatever lay to the west would belong to Castile; the rest, in practice, to Portugal.
John II of Portugal found that frontier stingy. His kingdom had spent decades sailing the Atlantic and skirting Africa, and he suspected a hundred leagues left too little room for his interests. Rather than accept the bull, he negotiated. The fruit of that diplomatic haggling was the treaty in question, which pushed the line far to the west: to 370 leagues west of the Cape Verde Islands. A single number, corrected across a negotiating table, and with it the fate of whole continents changed.
The power —and the trap— of words
It is worth pausing on what a treaty really is: a text. And every text is drafted, copied, translated and interpreted. Two copies of the agreement were made, each crown keeping its own; today the Portuguese exemplar is held at the Arquivo Nacional da Torre do Tombo in Lisbon and the Castilian one at the Archivo General de Indias in Seville. In 2007 both documents were jointly inscribed by Spain and Portugal on UNESCO's Memory of the World register, a rare distinction for a pact that once set two kingdoms against each other.
The trouble was that the treaty's words were at once precise and slippery. The line was defined in leagues, a unit that had no single, universally agreed value at the time: the Castilian league was not the Portuguese one, and even the equivalence between league and degree was disputed among cosmographers. Worse still, the text ordered the 370 leagues to be counted "west of the Cape Verde Islands", but that archipelago stretches across several degrees, and it was never specified which of its islands the measurement should start from. Each point of departure shifted the frontier by dozens of leagues.
On top of all this came an obstacle that the technology of the day could not overcome: there was no reliable way to calculate longitude at sea. Latitude could be worked out from the height of the sun or stars; fixing an exact meridian over an empty ocean, however, lay beyond the reach of fifteenth-century pilots. The Tordesillas line was, strictly speaking, an imaginary border that nobody knew how to draw with certainty.
When interpretation decides continents
That an ambiguous text should carve up the planet has unforeseeable results. The most discussed is Brazil. When Pedro Álvares Cabral reached its coast in 1500, those lands fell —by the Portuguese reading of the line— on the Lusitanian side, which is why Brazil speaks Portuguese and not Spanish. Some historians have suggested that Portugal already sensed the existence of lands to the west when it negotiated the 370 leagues; it is a debated hypothesis, best presented as such rather than as fact, yet it shows how the wording of a single clause could anticipate or foreclose empires.
Decades later, the problem resurfaced on the opposite side of the globe. If a line divided the Atlantic, where did its continuation fall on the far side of the world, in the coveted spice archipelago? The dispute over the Moluccas forced the signing, in 1529, of the Treaty of Zaragoza, which drew a complementary antimeridian. Tordesillas, conceived for one ocean, had ended up affecting the whole sphere.
From Tordesillas to today's treaties
Tordesillas was not an isolated case but the opening of a long history in which translation and diplomacy walk arm in arm. For centuries Latin served as the lingua franca of European treaties, until French displaced it as the language of diplomacy in the early modern age. The decisive turn came in 1919 with the Treaty of Versailles, drawn up as an authentic text in French and English at once: two versions of equal legal force, which meant they had to say exactly the same thing in two different languages. There, in its modern form, is born the very problem that was already looming in 1494 — how to guarantee that several versions of a pact mean one single thing.
International law eventually answered it. The Vienna Convention on the Law of Treaties of 1969 devotes its Article 33 to treaties authenticated in several languages: in principle the text is equally authoritative in each language, and when a comparison reveals a difference of meaning that interpretation cannot resolve, the meaning adopted is the one that best reconciles the texts in the light of the treaty's object and purpose. The United Nations works today in six official languages, with armies of translators whose job is precisely that: to ensure that the word agreed upon does not change as it crosses from one language into another.
One document, many hands
Behind that parchment there were not only kings. There were secretaries who chose every term, jurists who weighed the reach of every verb, cosmographers who argued over leagues and degrees, and copyists who reproduced the text so that each court could keep its own version. The treaty was ratified separately —Castile confirmed it on 2 July 1494 and Portugal on 5 September— because every word mattered enough to be checked twice.
That is perhaps the most enduring lesson of Tordesillas for those of us who work with texts. A document is worth not its solemnity but its precision: it must say exactly what it means, leaving no margins another party can widen in its favour. Five centuries on, when a text must take effect before an administration or a court —the province today of official sworn translation— the demand is unchanged: no ambiguity should decide for us what the words ought to have settled.