Navigation is the art of taking ships from one place to another whilst out of sight of land. Pilotage is doing the same thing whilst land and navigational aids are in sight. It is interesting to note that by the late 16th century all competent shipmasters were very experienced in the skills of pilotage, but navigation was the preserve of a small ‘aristocracy of experts whose business took them across the great oceans’ . Difficult harbours naturally required the employment of local experts. There was a quantum leap from being able to pilot ships to being able to navigate them well and this, together with possessing ships that were up to the demands of the task, was the great step forward made by European seafarers of these times. The main tools of the trade were the magnetic compass and the lead. The taking of depth soundings, even when out of sight of land, was an important addition to the knowledge gained from simple compass readings. Obviously, when landmarks were in sight, it was possible to fix a position easily. Most sailings were carried out within sight of the land – not too close where there were dangerous rocks and reefs, but close enough to be able to identify the Capes and headlands. It is interesting to note that a course that involved coastal sailing was sometimes called the ‘caping’ of the ship.
At first, most shipmasters were illiterate and needed to remember all the coastal details, bearings and positions, but later, when they became more literate, they were able to use books of written instructions known as sailing directions, otherwise known as portolani or rutters (French: routiers). Originally they were kept in pilots notebooks and then passed around, they became very valuable documents representing great accumulations of experience and knowledge. Sometimes they included instructions for long passages of up to seven or eight hundred miles between easily recognisable points. Knowledge of tides too became more and more important. In the Mediterranean, the navigators needed to know comparatively little about this, but in the north Atlantic around many coasts of Europe, tides were crucially important. One of the most difficult aspects of navigation was the measurement of distance travelled, which required knowledge of the ships speed. Methods were devised whereby a log was thrown off the back of a ship and pulled with it a rope, knotted at defined intervals. The speed could be calculated by counting the rate of passage of knots overboard, and timing them with a sandglass. The problem was in measuring time and knowing the speed of ocean currents, which was often very vague. Again, the wind might blow a ship off its designated course, making the calculation of its passage difficult. In sailing ships, the most crucial elements was the wind, of course and these were not always favourable. Tacking (sailing into the wind at an angle) was difficult in ships of moderate size up to the mid fifteenth century. As it became easier, a new method involving a device called a traverse board was devised for keeping track of distance travelled whilst on a given tack. These rough and ready methods were the only means available to navigators in the Atlantic until well into the seventeenth century.
As Parry  points out, by 1650, “the world outside Europe, as known to Europeans, was a world of coastlines, roughly charted, of scattered harbours connected by sea-borne communication.” It was a time when Europeans learned to think of the world as a single entity joined by oceans. Even so, the idea of erecting marine signposts at strategic locations along the coast was entirely missing. The unravelling of the science of navigation had still not been satisfactorily completed until the time when, in 1764, Harrison had satisfied the criteria for the Board of Longitude with his chronometer that enabled accurate calculations of longitude. (Captain James Cook took four chronometers with him on his second voyage of discovery in the Pacific. Only one was Harrison's and it was the only one that worked. It enabled Cook to accurately plot the positions he visited and to prove conclusively that the long-proposed Terra Australis Incognita did not exist in the place that had been proposed.) It may be that this too was another important reason why lightstructures were such a late addition to modern navigation practices. Thus, In a sense, we could argue that the use of lightstructures by a culture is but one measure of the degree to which civilisation has advanced. On the other hand, there are so many examples of ancient cultures being excellent sea-travellers that it could be argued that their sailors had such a good knowledge of astronomy that lightstructures were unnecessary for navigation at night.