By the second half of the fifteenth century, European monarchies had increased both their authority and their resources and were in a position to turn their energies beyond their borders.
For France, that meant the invasion of Italy, but for Portugal, a state not strong enough to pursue power in Europe, it meant going abroad.
The Spanish monarchy was strong enough by the sixteenth century to pursue power both in Europe and beyond.
At the same time, Europeans had achieved a level of wealth and technology that enabled them to make a regular series of voyages beyond Europe.
With details on coastal contours, distances between ports, and compass readings, these charts proved of great value for voyages in European waters.
But because the portolani were drawn on a flat scale and took no account of the curvature of the earth, they were of little use for longer overseas voyages.
Only when sea-farers began to venture beyond the coast of Europe did they begin to accumulate information about the actual shape of the earth.
By the end of the fifteenth century, cartography had developed to the point that Europeans possessed fairly accurate maps of the known world.
One of the most important world maps available to Europeans at the end of the fifteenth century was that of Ptolemy, an astronomer of the second century.
Printed editions of Ptolemy’s Geography, which contained his world map, became available from 1477 on.
In addition to showing the oceans as considerably smaller than the landmasses, Ptolemy had also drastically underestimated the circumference of the earth, which led Columbus and other adventurers to believe that it would be feasible to sail west from Europe to reach Asia.
The first European fleets sailing southward along the coast of West Africa had found their efforts to return hindered by the strong winds that blow steadily from the north along the coast.
By the late fifteenth century, however, sailors had learned to tack out into the ocean, where they were able to catch westerly winds in the vicinity of the Azores that brought them back to the coast of western Europe.
Christopher Columbus used this technique in his voyages to the Americas, and others relied on their new knowledge of the winds to round the continent of Africa in search of the Spice Islands.