The estuary of the Rio Paraná and Rio Uruguay, occasionally called "River Plate" by people versed in British naval history.

During the most recent Ice Age, the world's oceans were greatly shrunken, revealing the continental shelves hundreds of miles away from today's coastlines. The southern Atlantic coast of South America extended out as far as the Islas Malvinas. A little further up the coast, the great Rio Paraná drained the southern rain forest as well as the pampas (The Uruguay was probably a tributary of the Paraná at this time).

As the ice melted in the Northern Hemisphere and around Antarctica, the Atlanic Ocean rose, drowning the river valley, forming an embayment in the South Amercan coastline. The river's delta migrated up into the estuary until it it became indistingushable from its floodplain. A swampy tangle of distributaries and yazoos now stretches hundreds of miles up the Parana valley in Argentina, almost to Resistencia and Correntes on the border with Paraguay. Rio Paraná and Rio Uruguay turn Rio de la Plata brown with their sediment.

The area was inhabited even as the ice was melting. A little further into the interior, the Guarani tribe set up the first agricultural society in South America.

  • 1502 Amerigo Vespucci sailed by.
  • 1516 Juan Diaz de Solis explored the estuary, naming it "Mar Dulce". Guarani Indians eventually killed de Solis and most of his expedition.
  • 1520 Ferdinand Magellan hoped that the estuary was a route to the South Sea.
  • 1526 Sebastian Cabot, in the employ of Seville merchants, sailed up the Paraná. After trading with the Guarani for silver trinkets, Cabot renamed it "River of Silver".
  • 1536 Pedro de Mendoza founded Santa Maria del Buen Aire, but Mendoza died the following year on the trip home. The settlers abandoned the settlement, moving upriver to found Asunción. The Spanish found little silver along Rio de la Plata, and the province became a center for cattle and sheep ranching. Few settlers came from Spain; most were leftovers from the richer provinces of Peru, Chile, and Paraguay.
  • 1542 Phillip II set up the Viceroyalty of Peru, including Rio de la Plata.
  • 1580 Buenos Aires was refounded from Paraguay.
  • 1624 Disease decimated the Charrua who had fiercely kept the spanish out of Uruguay.
  • 1680 Portuguese settlers from Brazl founded Colonia del Sacramento on the north shore, to compete with Buenos Aires.
  • 1717 In response, the Spanish set up a military post on the north shore. In 1724, Don Mauricio Zabala promised settlers land and cattle, and Montevideo became a real town.
  • 1776 Philip IV and Jose de Galvez set up the Viceroyalty of Rio De la Plata, including Paraguay, Uruguay, Argentina, and the parts of modern-day Brazil controlled by Spain.
  • 1804 Napoleon Bonaparte replaced the King of Spain with his brother Joseph; the Spanish colonial system began to fall apart. In 1806 Great Britain sent a force to occupy Buenos Aires, to keep its resources out of Napoleon's hands. Spain had no troops, but an army set up by the creole viceroys threw the British out. However, Spanish control of the area was nil. After fighting between the creoles and the supporters of Ferdinand VII, Argentina and Uruguay each achieved their independence (1821 and 1825).
  • 1939 The British fleet trapped the German battleship Graf Spee in Montevideo Harbor, neutral waters which they had to respect. So did the Germans; Graf Spee was only permitted a short time in Montevideo. A British fleet waited for it to leave, but when the deadline arrived, the captain scuttled the ship rather than surrender it.