Trade provides mankind's most significant meeting place, the market. In primitive societies only religious events - cult rituals, or rites of passage such as marriage - bring people together in a comparable way. But in these cases the participants are already linked, by custom or kinship.
The process of barter brings a crowd together in a more random fashion. New ideas, along with precious artefacts, have always travelled along trade routes. And the natural week, the shared rhythm of a community, has frequently been the space between market days.
Agricultural produce and everyday household goods tend to make short journeys to and from a local market. Trade in a grander sense, between distant places, is a different matter. It involves entrepreneurs and middlemen, people willing to accept delay and risk in the hope of a large profit. The archive found at Ebla gives a glimpse of an early trading city, from the middle of the third millennium BC.
When travel is slow and dangerous, the trader's commodities must be as nearly as possible imperishable; and they must be valuable in relation to their size. Spices fit the bill. So do rich textiles. And, above all, precious ornaments of silver and gold, or useful items in copper, bronze or iron.
As the most valuable of commodities (in addition to being compact and easily portable), metals are a great incentive to trade. The extensive deposits of copper on Cyprus bring the island much wealth from about 3000 BC (Cyprus, in Latin, gives copper its name - cyprium corrupted to cuprum).
Later, when the much scarcer commodity of tin is required to make bronze, even distant Cornwall becomes - by the first millennium BC - a major supplier of the needs of Bronze Age Europe.
Waterborne traffic: 3000-1000 BC
By far the easiest method of transporting goods is by water, particularly in an era when towns and villages are linked by footpaths rather than roads. The first extensive trade routes are up and down the great rivers which become the backbones of early civilizations - the Nile, the Tigris and Euphrates, the Indus and the Yellow River.
As boats become sturdier, coastal trade extends human contact and promotes wealth. The eastern Mediterranean is the first region to develop extensive maritime trade, first between Egypt and Minoan Crete and then - in the ships of the intrepid Phoenicians - westwards through the chain of Mediterranean islands and along the north African coast.
Phoenicia is famous for its luxury goods. The cedar wood is not only exported as top-quality timber for architecture and shipbuilding. It is also carved by the Phoenicians, and the same skill is adapted to even more precious work in ivory. The rare and expensive dye, Tyrian purple, complements another famous local product, fine linen. The metalworkers of the region are famous, particularly in gold. And Tyre and Sidon are known for their glass.
These are only the products which the Phoenicians export. As traders and middlemen they take a cut on a much greater cornucopia of precious goods - as the prophet Ezekiel grudgingly admits.
The caravan: from 1000 BC
In the parched regions of north Africa and Asia two different species of camel become the most important beasts of burden - the single-humped Arabian camel (in north Africa, the Middle East, India) and the double-humped Bactrian camel (central Asia, Mongolia). Both are well adapted to desert conditions. They can derive water, when none is available elsewhere, from the fat stored in their humps.
It is probable that they are first domesticated in Arabia. By about 1000 BC caravans of camels are bringing precious goods up the west coast of Arabia, linking India with Egypt, Phoenicia and Mesopotamia.
This trade route brings prosperity to Petra, a natural stronghold just north of the Gulf of Aqaba on the route from the Red Sea up to the Mediterranean coast. In the heyday of the kingdom of Israel, around 1000 BC, this important site is occupied by the Edomites - bitter enemies of the Israelite kings, David and Solomon.
In the 4th century BC the Edomites are displaced by an Arab tribe, the Nabataeans. They soon come into conflict with new neighbours in Mesopotamia, the Seleucid Greeks, who have an interest in diverting trade from the Gulf of Aqaba.
New routes to the west: from 300 BC
The presence of Greeks in Mesopotamia and the eastern Mediterranean encourages a new trade route. To ease the transport of goods to Greece and beyond, Seleucus founds in 300 BC a city at the northeast tip of the Mediterranean. He calls it Antioch, in honour of his own father, Antiochus. Its port, at the mouth of the river, is named after himself - Seleucia.
Here goods are put on board ship after arriving in caravans from Mesopotamia. The journey has begun in another new city, also called Seleucia, founded in 312 BC by Seleucus as the capital of his empire. It is perfectly placed for trade, at the point where a canal from the Euphrates links with the Tigris.
Doura-Europus, a frontier town: from the 3rd century BC
The first major stopping point for the caravans on the route from Mesopotamia to Syria is the old Babylonian town of Doura, on the west bank of the Euphrates. Rebuilt by Seleucus in about 300 BC, it is given the new name of Europus.
This settlement later becomes of great importance as a frontier post, when the Euphrates is the boundary between successive empires.
Palmyra: from 300 BC
The other great staging post on the route to Antioch is also an important site, and today a much more visible one. It is Palmyra, famous as one of the great ruined classical cities.
From Doura-Europus, on the Euphrates, the caravans strike west through the desert to the Mediterranean coast. Palmyra is an oasis half way across this difficult terrain. Its wealth derives from its position on the east-west axis from Persia to the coast, in addition to being on the older routes up from Mesopotamia. In the 1st century BC, when Palmyra is on the verge of its greatest prosperity, a rich new supply of goods begins to arrive from the east along the Silk Road. But by now neither Persia nor Mesopotamia are Greek.
A trade route from China: 2nd century BC
A tentative trade route is becoming established along a string of oases north of the Himalayas. They are very exposed to the broad expanse of steppes - from which marauding bands of nomadic tribesmen are liable to descend at any moment - but protection by the Han dynasty in China is now making it reasonably safe for merchants to send caravans into this region. The goods are usually unloaded in each oasis and traded or bartered before continuing the journey westwards - where rich customers around the Mediterranean are eager for the luxury products of the east.
In 106 BC, for the first time, a caravan leaves China and travels through to Persia without the goods changing hands on the way. The Silk Road is open.
In the 1st century BC the Romans gain control of Syria and Palestine - the natural terminus of the Silk Road, for goods can move west more easily from here by sea. Soon a special silk market is established in Rome.
China, proudly self-sufficient, wants nothing that Rome can offer. And the Han rulers are unwilling to release silk - either as thread or woven fabric - except in exchange for gold. It has been calculated that in the 1st century AD China has a hoard of some five million ounces of gold. In Rome the emperor Tiberius issues a decree against the wearing of silk. His stated reason is the drain on the empire's reserves of gold. The Silk Road introduces global economics.
World trade: from the 1st century AD
The Silk Road links east Asia and western Europe at a time when each has, in its own region, a more sophisticated commercial network than ever before.
The caravan routes of the Middle East and the shipping lanes of the Mediterranean have provided the world's oldest trading system, ferrying goods to and fro between civilizations from India to Phoenicia. Now the Roman dominance of the entire Mediterranean, and of Europe as far north as Britain, gives the merchants vast new scope to the west. At the same time a maritime link, of enormous commercial potential, opens up between India and China.
The map of the world offers no route so promising to a merchant vessel as the coastal journey from India to China. Down through the Straits of Malacca and then up through the South China Sea, there are at all times inhabited coasts not far off to either side. It is no accident that Calcutta is now at one end of the journey, Hong Kong at the other, and Singapore in the middle.
Indian merchants are trading along this route by the 1st century AD, bringing with them the two religions, Hinduism and Buddhism, which profoundly influence this entire region.
The trading kingdoms of West Africa: 5th - 15th c. AD
A succession of powerful kingdoms in West Africa, spanning a millennium, are unusual in that their great wealth is based on trade rather than conquest. Admittedly much warfare goes on between them, enabling the ruler of the most powerful state to demand the submission of the others. But this is only the background to the main business of controlling the caravans of merchants and camels.
These routes run north and south through the Sahara. And the most precious of the commodities moving north is African gold.
The first kingdom to establish full control over the southern end of the Saharan trade is Ghana - situated not in the modern republic of that name but in the southwest corner of what is now Mali, in the triangle formed between the Senegal river to the west and the Niger to the east.
Ghana is well placed to control the traffic in gold from Bambuk, in the valley of the Senegal. This is the first of the great fields from which the Africans derive their alluvial gold (meaning gold carried downstream in a river and deposited in silt, from which grains and nuggets can be extracted).
Like subsequent great kingdoms in this region, Ghana is at a crossroads of trade routes. The Saharan caravans link the Mediterranean markets to the north with the supply of African raw materials to the south. Meanwhile along the savannah (or open grasslands) south of the Sahara communication is easy on an east-west axis, bringing to any commercial centre the produce of the whole width of the continent.
While gold is the most valuable African commodity, slaves run it a close second. They come mainly from the region around Lake Chad, where the Zaghawa tribes make a habit of raiding their neighbours and sending them up the caravan routes to Arab purchasers in the north.
Other African products in demand around the Mediterranean are ivory, ostrich feathers and the cola nut (containing caffeine and already popular 1000 years ago as the basis for a soft drink).
The most important commodity coming south with the caravans is salt, essential in the diet of African agricultural communities. The salt mines of the Sahara (sometimes controlled by Berber tribes from the north, sometimes by Africans from the south) are as valuable as the gold fields of the African rivers. Traders from the north also bring dates and a wide range of metal goods - weapons, armour, and copper either in its pure form or as brass (the alloy of copper and zinc).
These various goods, travelling some 1200 miles from one end of the trade route to the other, rarely go in a single caravan for the whole distance. They are unloaded and packed on to new transport, as specialists undertake each very different section of the journey - to the edge of the desert (either from the Mediterranean coast or from the African forest and savannah) and then from oasis to oasis through the Sahara.
In the same way goods are likely to be bought and sold on the route by specialist middlemen, with whom merchants naturally establish their own regular contacts. In this way trading partnerships develop, often made up of members of the same community or even a single family.
Vikings in Russia: from the 9th century AD
Unusually for the Vikings, trade rather than plunder is the main reason for their penetration deep into Russia during the 9th century AD. The rivers of eastern Europe, flowing north and south, make it surprisingly easy for goods to travel between the Baltic and the Black Sea.
One spot is particularly well-favoured as a trading centre. Near Lake Ilmen the headwaters of the Dvina, Dnieper and Volga rivers are close to each other. Respectively they flow into the Baltic, the Black Sea and the Caspian. Goods ferried by water between these important trading regions converge on this area. By the early 9th century Viking tribes known as the Rus have a base on the site of Novgorod.
Although they are not Slavs, there is justice in the Rus giving Russia her name. Their development of trade, particularly down the Dnieper (a route which becomes known as Austrvegr, or the 'Great Waterway'), lays the foundation of the Russian nation.
In 882 a Viking leader, Oleg, moves his headquarters down the Dnieper, seizing the town of Kiev. Here, in 911, he negotiates a commercial treaty with the Byzantine empire.
A Viking successor of Oleg's in Kiev, two generations later, describes how this first Russian city is the centre of a triangular trade between civilized Byzantium in the south, the steppe lands in the middle, and the wild forests of the north.
In this place 'all goods gather from all parts: gold, clothes, wine, fruits from the Greeks; silver and horses from the Czechs and Hungarians; furs, wax, honey and slaves from the Rus'.
The Pax Mongolica and the Silk Road: 13th - 14th c. AD
By the middle of the 13th century the family of Genghis Khan controls Asia from the coast of China to the Black Sea. Not since the days of the Han and Roman empires, when the Silk Roadis first opened, has there been such an opportunity for trade. In the intervening centuries the eastern end of the Silk Road has been unsafe because of the Chinese inability to control the fierce nomads of the steppes (nomads such as the Mongols), and the western end has been unsettled by the clash between Islam and Christianity.
Now, with the Mongols policing the whole route, there is stability. In an echo of the Pax Romana, the period is often described as the Pax Mongolica.