The Treaty of San Ildefonso: Portugal and Spain redraw South America, 1777

On 3 June 1777 the Portuguese garrison of Colónia do Sacramento lined up unarmed in the main square, packs on their backs. Outside the walls a Spanish army had dug in around the town. When the siege began, the garrison had food for about five days. Their governor, Colonel Francisco José da Rocha, had decided to hand the town over before its defenders and people starved.1 source

Father Pedro Pereira Fernandes de Mesquita, the bishop's vicar in Colónia and chaplain of its cavalry regiment, watched them go. He wrote his account in Buenos Aires the following year.1 source

According to a Spanish diary of the siege, the next day a Spanish marshal, Victorio de Navia, took possession of the town in the name of Charles III. A Te Deum was sung in the parish church and on 7 June the demolition of the walls began. For almost a century Colónia had been Portugal's foothold on the River Plate.1 source

Four months later, on 1 October 1777, two diplomats signed a treaty at San Ildefonso, a Spanish royal palace near Segovia. One was Francisco Inocêncio de Sousa Coutinho, Portugal's ambassador to Madrid. The other was the Count of Floridablanca, Spain's first secretary of state. Their 25 articles turned the loss of Colónia into law and drew a new line across South America.3 sources

The quarrel was old. In 1494 the Treaty of Tordesillas had split the world outside Europe between the two crowns along a north–south line in the Atlantic. On paper, the Amazon lay on Spain's side. In practice, Portuguese settlers and soldiers in Brazil pushed far beyond the line, and by the eighteenth century it no longer matched anything on the ground.3 sources

Colónia was the sharpest point of that push. Manuel Lobo founded it in 1680 on the northern shore of the River Plate, in what is now Uruguay, on the orders of the prince regent Pedro. The aim was to reach the silver of Potosí, smuggled down the estuary and shipped to Lisbon through Brazilian ports. Spanish colonial troops and Guarani soldiers from the Jesuit missions destroyed it eight months later.2 sources

Then a pattern set in. Portugal lost the town in war and won it back at the peace table: by a provisional treaty in 1681, at Utrecht in 1715 and at Paris in 1763. In between, Buenos Aires besieged it from October 1735 to September 1737 and kept a fortified blockade line around it for decades. Smugglers sold silver, hides, horn, tallow and yerba mate through its gates.2 sources

In 1750 the two crowns tried a clean break. The Treaty of Madrid, signed on 13 January, scrapped Tordesillas and adopted uti possidetis: each side kept what it actually held, with borders following big rivers and mountain ridges. That gave Portugal most of the Amazon and Spain the River Plate. Portugal also agreed to swap Colónia for seven Jesuit mission towns east of the Uruguay river, the Sete Povos das Missões.3 sources

The Guarani refused to go. In February 1753 their militia stopped the first boundary party at Santa Tecla, a ranch belonging to the town of São Miguel. In the war that followed, a joint Spanish and Portuguese army killed the Guarani leader Sepé Tiaraju on 7 February 1756 and won the battle of Caiboaté three days later. The two armies then occupied the mission towns.2 sources

In Portugal people protested at giving up Colónia. In Spain they protested at giving up the missions. The death of Ferdinand VI in 1759 brought Charles III to the Spanish throne and a change of course, and on 12 February 1761 the Treaty of El Pardo annulled it. The border went back to where it had been before 1750, with Spain in the missions and Portugal in Colónia.4 sources

Peace did not last. In the Seven Years' War, when Spain and Portugal fought on opposite sides, the governor of the River Plate, Pedro de Cevallos, took Colónia in 1762 and the Portuguese town of Rio Grande de São Pedro, at the mouth of the Lagoa dos Patos, in 1763. The Treaty of Paris forced Spain to return Colónia, but Spain kept Rio Grande, arguing that the Portuguese had built it on Spanish land.1 source

Portugal took Rio Grande back in an offensive of the mid-1770s, with large numbers of men recruited in Brazil and Portugal. The build-up frightened Buenos Aires. At the end of 1776 the governor of Colónia reported that the Spanish city had only a hundred paid soldiers and was in “great unrest and fear” of a Portuguese invasion.1 source

Madrid answered with an invasion force. A fleet left Cádiz on 13 November 1776 with more than 11,500 men on board, under Cevallos, now named viceroy of the River Plate. In February 1777 it anchored off the island of Santa Catarina, on the coast of southern Brazil. The garrisons of the island's forts left their posts and fled to the mainland, and 523 Portuguese soldiers were taken as prisoners of war.1 source

Storms scattered the fleet off Rio Grande and saved the town. While still at Santa Catarina, Cevallos heard that the king of Portugal had died. Expecting the two courts to make peace and stop him, he sailed at once for Colónia, which his ships had already cut off from Rio de Janeiro. Captured letters told him how short of food the town was.1 source

Rocha surrendered in early June. The historian Paulo Possamai, citing J. C. Rego Monteiro's 1937 history of Colónia, writes that Rocha held a secret order from Pombal to give up the town after putting up a show of defence. Cevallos then shipped the civilians across the river and scattered them to frontier villages such as Luján, Areco, Arrecifes and Pergamino. Colónia's soldiers were sent inland to Córdoba, and the men captured at Santa Catarina to Mendoza.1 source

The news that Cevallos heard was true. King José I had died at Ajuda, in Lisbon, on 24 February 1777. Throughout his reign his chief minister, Sebastião José de Carvalho e Melo, Marquis of Pombal, had run Portugal, rebuilt Lisbon after the 1755 earthquake and expelled the Jesuits. The new queen was José's daughter, Maria I, and Pombal was soon banished to his estates at Pombal.2 sources

Maria's family pulled towards Madrid. Her mother, Mariana Vitória, was a Spanish princess, a daughter of Philip V. Her match with José was arranged in 1727 and the wedding held in January 1729. That made Charles III of Spain the new queen's uncle, and in her letter of ratification Maria called him “my good brother and uncle”. The historian Simei Torres describes the change of reign as the moment Portugal, weakened, set out to mend relations with its neighbour.4 sources

Portugal was in no position to bargain. Colónia had fallen and Spanish troops held Santa Catarina. Peace in the south would cost Lisbon most of what it had fought for on the River Plate.2 sources

The preamble spoke of ending discord that had lasted “almost three centuries” over the two crowns' lands in America and Asia. It called itself preliminary: a basis for a definitive treaty to be written once the frontier had been surveyed. Article I declared perpetual peace by land and sea, with “total forgetting of the past”, and confirmed the peace treaties of 1668, 1715 and 1763. Article II freed all prisoners.2 sources

In the south the line broadly followed 1750, but without the swap. Spain kept Colónia and the missions, and the Plate became a Spanish river. Portugal kept Rio Grande and the coast up to Santa Catarina. Between them lay a no man's land of lagoons and coastal strips. Further north, the treaty traced the border along the Iguaçu, Paraná, Paraguay, Guaporé and Madeira rivers to the Amazon, close to the 1750 line.3 sources

The Santa Catarina clause shows what worried Spain. Portugal had to promise that at no time, in peace or in any war it took no part in, would it let a foreign squadron, warship or merchant ship into the harbour of Santa Catarina or the nearby coast, above all ships of a power at war with Spain or suspected of smuggling.1 source

In the nineteenth century the Brazilian historian Francisco Adolfo de Varnhagen judged the deal harshly.2 sources

Spain wanted one more thing, and got it in a second treaty signed at El Pardo on 11 March 1778. Article 13 said that, to “compensate in some way” for the cessions, restitutions and renunciations Spain had made in 1777, Portugal ceded the island of Annobón and its rights to the island of Fernando Pó, now Bioko, in the Gulf of Guinea.2 sources

The main purpose was the slave trade. The article opened by saying both monarchs wished to promote the buying and selling of enslaved Africans by their subjects without the harmful contracts once given to Portuguese, French and English companies. Spain's colonies in America needed labour, and Spanish ships could now trade on the African coast opposite the islands, in the Gabon and Cameroon rivers.1 source

The Spanish expedition sent in April 1778 under the Count of Argelejo to take possession achieved almost nothing, and the islands' reputation for disease kept Spain away for decades. Spanish rule over Fernando Pó and Annobón was only imposed by Juan José de Lerena's expedition of 1843. The islands are now part of Equatorial Guinea.2 sources

Article XV ordered joint commissions to walk the frontier, mark it and map it. The two courts split the work among four parties, from the Atlantic coast in the south to the Amazon in the north. Each was meant to have two principal commissioners, two engineers, two geographers and two local guides.3 sources

They were slow to start. Spanish officials later complained that Madrid named its commissioners in 1778 and Lisbon not until 1783. Lisbon replied that its men had sailed with the Spanish officers in 1782 and that its first commissioner had been in Rio Grande as governor since 1781. Guarani from the mission towns helped locate the line, supplied the survey parties and patrolled the undivided lands between the two crowns.1 source

In the Amazon a Portuguese party of about 500 people gathered on the Rio Negro in October 1780. The Spanish team of about 300, under Colonel Francisco Requena, arrived from Maynas, in today's Peru, in April 1781. The two parties made the village of Ega, on the Solimões, their base and spent a decade arguing over rivers, until the Spanish withdrew in 1791 with the work unfinished.2 sources

In the south the dispute was over which stream was the Pepiri-guaçu. In 1788 the Spanish commissioners found a river further east and claimed that the surveyors of 1759–60 had picked the wrong one. Their river would have moved the border well to the east, across the land between the Uruguay and Iguaçu rivers. The question was still open when war came.1 source

Colónia's people paid first. Rocha stayed with his men in Buenos Aires until August 1778, then led those who wanted to leave back overland to Rio Grande. In Rio de Janeiro his own officers accused him over the surrender. He was sent to Lisbon, tried and sentenced to death, and the sentence was commuted to exile for life in Angola, where he died.1 source

So many families from Colónia arrived in Rio Grande in 1779 that the governor, José Marcelino de Figueiredo, wrote in May that he had nothing to give them. He shared out land, some of it on the plains by the São Gonçalo channel. Settlers from Colónia and the Atlantic islands there later asked for a parish of their own, and in 1812 São Francisco de Paula was created, the nucleus of today's city of Pelotas.1 source

The treaty itself died in 1801. On 25 February Spain declared war on Portugal and ordered its officers in South America to open hostilities against Brazil. Luso-Brazilian forces overran the whole east bank of the Uruguay above the Quaraí river, including the old mission towns, and pushed south to the Jaguarão river and the Mirim lagoon.1 source

The peace signed at Badajoz on 6 June 1801 said nothing about America. It neither restored the situation before the war nor revived the 1777 treaty, so Portugal kept what it had taken. The Sete Povos, which the Guarani had died defending in 1756, became part of Brazil after all.1 source

Look at a map of Brazil's far south today and you can still read the 1777 line in places. The Plate is not Brazilian, Colónia is a town in Uruguay, and the Lagoa Mirim, part of the 1777 buffer zone, has been split between Brazil and Uruguay since a treaty of 1909. Santa Catarina island, handed back under article XXII, is home to Florianópolis, the capital of the state of Santa Catarina.2 sources

The treaty also outlived itself in court. When Brazil and Argentina argued in the 1880s and 1890s over the land between the Uruguay and Iguaçu rivers, now in the west of Santa Catarina state, the case turned on which river was the Pepiri-guaçu, the question the surveyors of 1788 had left open. Brazil's advocate, the Baron of Rio Branco, argued among much else from an authenticated copy of the Mapa das Cortes, the map used for the 1750 treaty, and on 5 February 1895 the arbitrator, US president Grover Cleveland, found for Brazil.2 sources

For Portugal, 1777 marked the end of a long gamble on the River Plate. The smuggling base it had fought over for almost a century was gone, and the future of the south lay in Rio Grande, settled in part by the people expelled from Colónia.1 source