A Marinharia dos Descobrimentos: technology, method, and a hunger to know

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A Marinharia dos Descobrimentos: technology, method, and a hunger to know<br>The Portuguese Discoveries were not magic, but method. An old navigation book showed me astrolabes, star charts, and practical technology at sea. Here’s a glimpse of it.<br>João Tomé<br>Jun 22, 2026

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For years I’ve wanted to write something substantial about science and technology in the age of the Portuguese Discoveries, in the 15th and 16th centuries. What always interested me most was how it all came together through science, human drive, and technology. I had been slowly accumulating books, podcast episodes (some with me hosting), notes, and references.<br>Then, in a brief exchange on Twitter a few days ago, I asked Jorge Ventura, an Azorean navigator and author, if he had any reading suggestions, and he pointed me to A Marinharia dos Descobrimentos , by A. Fontoura da Costa (from the 1930s). It was exactly the right recommendation.<br>This is still not it (the full “writing”, I mean), but it’s a start.

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Leafing through the book, I found precisely the kind of material that fascinates any geek with a taste for history. Not sweeping abstractions about national destiny or heroic “epic” narrative, for which we already have Camões’s Os Lusíadas or the stories of Fernão Mendes Pinto, but objects, diagrams, and technical solutions to very concrete problems. What stands out most is that the Portuguese did not advance through magic, nor through some sudden explosion of isolated genius. They advanced because they took existing technology and made it work at sea.

Astrolabes reproduced in A Marinharia dos Descobrimentos: inherited technology adapted for Portuguese nautical use.

The astrolabe is the obvious example. It was not a Portuguese invention, yet it appears here as a working tool, almost like repurposed hardware adapted for an extreme environment. The same can be said of astronomical navigation more broadly: diagrams of Polaris, constellations, and sky-reading schemes, visual guides for astronomical orientation, which in practice turned the night into a usable interface.

Astronomical orientation scheme based on Polaris and the constellations: the sky as a navigational interface.

The hourly or equatorial rose for tides: a conceptual device linking direction, time, the Sun, the Moon, and the tide.

But there are even better details. One of them is the so-called hourly or equatorial rose for tides. It is not just a compass rose: it is a conceptual device for relating direction, the Sun, the Moon, time, and tidal movement. Almost a small analog computer. Another is the succession of maps and charts in imperfect and corrected versions, where you can actually watch knowledge being refined iteratively, as if you were looking at successive builds of a cartographic system still in debug mode.

Chart of the island of São Lourenço, now known as Madagascar: cartography as an iterative process of observation, correction, and refinement.

It also helps to see that this technical explosion did not emerge from nowhere. First under Prince Henry, and later under John II, there was a political decision to create incentives to explore, measure, and profit. Henry sponsored voyages, brought together pilots, cartographers, and experts in nautical astronomy, and helped turn navigation into a sustained project.<br>John II was even colder and more effective, and he seems to have relished keeping things secret and out of Castilian hands, something Manuel I later diluted. He reinforced the royal monopoly over African trade, backed specialists such as José Vizinho and Abraham Zacuto, and made the search for a sea route to India a matter of state priority.<br>Another detail I especially like about this early phase of Portuguese expansion is that the Casa da Guiné, and later the Casa da Índia, which made that progress possible, were not modern private companies. They were Crown institutions set up to manage monopolies, organize fleets, gather information, control commodities, and turn discovery into revenue, while still leaving room for contracts and leases with private actors. One of my favorite stories from the Discoveries, in fact, took place not by sea but over land, in the lonely figure of the spy-explorer Pêro da Covilhã.

Pages on the Casa da Mina, the Casa da Índia, and nautical astronomy: navigation also meant organizing information.

And the engine behind all this was not merely scientific curiosity, though some certainly had that too. It was commerce, power, and religious legitimacy: gold, spices, direct routes, papal backing, evangelization, and prestige in the eyes of the clergy.<br>Once this model began to produce results, imitation was inevitable. Castile responded with Columbus, after he had been rejected by the Portuguese king, who may well already have suspected the existence of America, and perhaps even Brazil, and with its own...