The explorations undertaken from Latin Christendom in the period with which we are concerned were chiefly directed along five new long-range routes. Since each in turn dominated a distinct but overlapping phase of the story they can conveniently be dealt with successively. First, the exploration of the principal archipelagoes of the eastern Atlantic, which began towards the end of the thirteenth century or early in the fourteenth and which, though well advanced by the 1380s, was only finally accomplished in the mid-fifteenth century; secondly, the search for routes across and around the Sahara, which made little progress before the fifteenth century, but which was prolonged until the entire coast of Africa had been explored to beyond the Cape of Good Hope by 1488; thirdly, the investigation of a new route into and across the north Atlantic, which can be documented in some detail from the 1450s; next, the discovery of routes back and forth across the ocean in central latitudes, made by Columbus in 1492—3; and, finally, the early exploration of the south Atlantic and the opening of a route to the Indian Ocean.
The first of these phases was the work of modest miracles of high medieval technology: the cog, the compass, the marine chart and primitive celestial navigation, done by making rough assessments of relative latitude on the open sea through observation of the height of the sun or Pole Star with the naked eye. In the thirteenth century, when Mediterranean navigators overcame the intimidatingly adverse current that races through the Strait of Gibraltar and began to frequent the Atlantic in large numbers, some turned north to the lucrative and well-known markets of Flanders and England; others turned south into waters unsailed, as far as we know, for centuries, off the west coast of Africa. The record of only one such voyage has survived: the Vivaldi brothers’ attempted circumnavigation of Africa in Genoese galleys in 1291. They were never heard of again, but it is likely that there were other journeys in the same direction. It was probably in the course of such journeys that the Canary Islands were discovered, ‘memoria patrum’ according to Petrarch, writing in the 1340s. The first record of some of the Canaries, and perhaps of Madeira, occurs in a map of 1339. Records of voyages to the islands are prolific in the 1340s. One, which included references to Italian, Portuguese and Spanish participants, was copied by Boccaccio and dated 1341. From 1342, a series of voyages in vessels described as cocas or coques to ‘islands newly found in parts of the west’ was recorded in Majorcan documents. Despite gaps in the archives, these can be shown to have had a more or less continuous history until the 1380s, though the nature of the enterprise was transformed in its course, as, from 1352 onwards, missionaries replaced merchants as its prime movers. Visits to the Azores and Madeira group can be inferred both from the nature of the wind system, which tends to impose a daring passage out into the ocean on traffic returning from the Canaries, and from cartographical evidence, which suggests that all but the two most westerly islands of the Azores may have been known to mapmakers of the 1380s. In 1402 to 1405, the gold-hunting expedition of Bethencourt and La Salle contributed the first itinerary — transmitted in a form capable of being mapped — of an exploration by land, on the islands of Lanzarote and Fuerteventura. An exclusively Portuguese enterprise, intermittently pursued between 1427 and 1452, established the true relationship of the islands of the Azores to one another, enabled mapmakers to fix them in roughly their true positions, and added the two remotest islands, Flores and Corvo, to the known tally.