Esmeraldo de Situ Orbis, a Book of Secrets

Half-forgotten and out of sight for centuries, Esmeraldo de Situ Orbis (1505–1508), by Portuguese navigator and cosmographer Duarte Pacheco Pereira (1460–1533), is a technical treatise describing the African ports known by Portuguese mariners sailing to India, following Vasco da Gama’s (1469–1524) discovery of this nautical route (1497–1498).

Duarte Pacheco Pereira - Anonymous (17th century)

The “Prologue” of this veritable treasure chest of maritime rutters, which allowed King Manuel I (1495–1521) to rule the trade from Asia to Europe, offers to the historian of science an unexpected gift – the very modern idea that the wealth and fame of a kingdom is a consequence of scientific and technological achievements:

We can say that the glory of your victories and the praise of your name and great navigation and conquest is related to Menelaus & Hanno the Carthaginian & Eudoxus, whom the authors celebrate and mention so much, & also to all the Kings and princes your predecessors; & how in so little time your Highness has discovered almost one thousand and five hundred leagues beyond all the ancients and moderns that had never been known or navigated by any nations of our west (…).

By specifying the giants whose shoulders’ King Manuel is standing on, Pacheco Pereira sets the monarch’s success on two pillars. On one side, the author refers to Menelaus of Alexandria (c. 70–140 CE), a Greek astronomer and mathematician who studied the geometry of the sphere and how it can be applied to astronomical measurements and calculations; and to Eudoxus of Cnidus (c. 408 BCE–355 BCE), another Greek astronomer and mathematician, also dedicated to the study of spherical astronomy, crucial for Early Modern celestial navigation. On the other side, the author refers to Hanno the Navigator (c. 500 BCE), the mythical Carthaginian navigator and author of Periplus Hannonis, an itinerary detailing a voyage of exploration and colonization from Carthage down the coast of West Africa to the Gulf of Guinea, the type of text that precedes the oceanic rutter, certainly an inspiration to the Esmeraldo.

These pillars for the glory of Early Modern Portugal are, on the one hand, astronomy and mathematics, the scientific disciplines that allow for a pilot in the middle of the ocean to make a correct measurement of latitude. On the other hand, the practice itself of navigation, made possible by the pilot’s knowledge of celestial navigation using instruments — a practice guided by charts and rutters, the secret for the Portuguese kingdom to establish a maritime route made of safe, and repeated, roundtrip voyages, which ultimately led to the creation of a global empire. [Joana Lima]