Over the millennia, the growing importance of trade encouraged the development of new means of transport, which served first to connect, and then to integrate, distant regions.
A range of modes of transport served different environments. On land, the chief means were walking, riding and using draught animals to carry loads and to pull wagons. But water – whether rivers, lakes or sea – often offered faster routes than land (with its swamps, forests and broken ground), and often enabled greater quantities of goods to be transported. For land routes, key points were where rivers could be forded or bridged, or where passes pierced mountain ranges. Water transport called for navigable rivers and natural harbours, features that often dictated the location of human settlement. To this day many of the world’s most important cities have grown on a navigable river or a natural harbour. Although transport technology improved over the centuries, its basis remained much the same – dependent on human or animal muscle power, wind, or the flow of water – until steam power transformed land and sea transport in the 19th century.
The driving of livestock for sale at often distant markets helped to establish overland routes. These long journeys, often of hundreds of kilometres, caused the animals to lose weight and thus value, so they would be fattened again by grazing near markets. All of this drove up the cost of meat, so that only the wealthy could usually afford it. The staging of lavish feasts in traditional stories from around the world highlights how rare and desirable meat was.
Before the steam engine, travel by water depended on climate and weather. Winter freezing, spring snow-melt floods and summer drought all caused problems, as did natural silting, which could make rivers too shallow to navigate. In many fast-flowing rivers, it was impossible to use horses on the banks to pull boats upstream against the current. As a result, for example on the River Rhône in France, boats were built upstream then, once they had travelled downstream with their loads, would be broken up for timber.
At sea, storms were always a danger, while contrary winds and currents hampered travel. The circular or counter-circular directions both of prevailing winds and of ocean currents affected the spread of seaborne migratory or trade routes. For example, it was difficult to sail the southern Pacific from east to west as the current pushed boats northwards. In the Atlantic, the routes established by European navigators by the 17th century exploited the prevailing winds and currents, heading southwestward from Europe towards the Americas, and returning in a north-easterly direction, several hundred miles north of the outward route. The hazards involved in navigating over long distances also affected travel on the oceans. While early mariners could navigate to some extent via Sun and stars, and by using the magnetic compass introduced to Europe from China in the later Middle Ages, it would be many more centuries before they could identify their longitudinal position.
On land, animals were a key alternative to human porterage (common, for example, in sub-Saharan Africa and in the Andes mountain chain of South America). A range of different mammals were enlisted as draught animals in different parts of the world – oxen, horses, asses, elephants, various members of the camel family (see here ). At first, draught animals would either just carry or drag their loads (often on some kind of primitive sledge). The wheel brought a major advance (see here ), but in most parts of the world the absence of good roads (roads were usually quagmires in winter, and grooved by ruts in summer), let alone an integrated road system, still restricted overland movement. In many places, the construction of canal networks – able to carry greater loads – preceded the establishment of well-maintained road systems.