The city of Lisbon is perched on the north side of one of the most stunning estuaries in the world. The name comes from the Greek, a reflection of the diversity of ancient cultures that made it past the Pillars of Hercules and headed west up the Atlantic coast of Europe. How different it must have been from the Mediterranean navigation to which they were accustomed.

 Turning north from Cape Sao Vicente, where Prince Henry the Navigator is thought to have established his school of navigation, those ships braved strong tidal currents, and the full force of the Atlantic weather. Although smaller natural harbours exist, the two great ones are about 200 km up the coast, the estuaries of the Sado and Tejo (or Tagus). The Tagus estuary is large, with an area of 320 km2 – about 60,000 soccer fields.

The estuaries of the Tagus and Sado

The estuaries of the Tagus and Sado

The two estuaries were separated by the rise of the Arrabida mountain, millions of years ago, which turned the mouth of each is a narrow channel. Both estuaries have large nature conservancy areas, and are extremely beautiful.


It was in the Bairro Alto, one of the most emblematic neighborhoods of Lisbon, perched on one of the city’s seven hills, that much of the science of the Portuguese discoveries was discussed and prepared. Pero de Alenquer, the chief pilot who guided Vasco da Gama’s ships to India, and a veteran of many other journeys, is introduced in this chapter:

http://www.theindiaroad.com/blog/1486 – The Astronomer.pdf

The context is a set of lectures and discussions carried out by eminent astronomers of the day. Most of these were Sephardi Jews – King John II of Portugal encouraged a meritocracy, untainted by religious prejudice – in sharp contrast to his Spanish neighbours the Reyes Catolicos, or Catholic Kings, and their chief inquisitor Torquemada.


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