Gold is heavy, and the world is wide. Between the place a metal comes out of the ground and the place it becomes money, there is always a road. In the medieval world there were two of them, and this is the story of where they met.
The first ran north across the largest desert on earth. The second was not a road at all but a coin, struck in a city on the Bosphorus, which held its weight and its purity for roughly seven hundred years and was taken, without weighing, by merchants who had never heard of the emperor whose face was on it.
The road across the sand
Camels crossed the Sahara in antiquity, but the caravan trade reached what the World History Encyclopedia calls its golden period from the ninth century onwards. The Metropolitan Museum of Art dates the great age of the gold traffic from the seventh to the fourteenth century, and describes the shape of it plainly: Mediterranean economies wanted gold and could supply salt, sub-Saharan economies had gold in abundance and needed salt to live. By the eleventh century a typical caravan ran to a thousand camels.
The northern gate was Sijilmasa, an oasis city in what is now southeastern Morocco, where the desert crossing began and where West African gold was refined. The southern gate, in the great age of the empire of Ghana, was Awdaghust. Between them lay the salt.
The salt came out of Taghaza, and we have an eyewitness. The Moroccan traveller Ibn Battuta set out from Sijilmasa in February 1352 and reached Taghaza after twenty five days. In his account, recorded in the University of California, Berkeley's ORIAS summary of his travels, he stayed in a house built of salt. The village had houses and a mosque made of salt blocks, roofed with camel skins, in a place with no trees and nothing but sand. The miners dug the salt in thick slabs. A camel carried two of them.
How much gold a slab of salt was worth is where the sources part company, and it is worth saying so. The Metropolitan Museum records that salt was so valuable south of the desert that it was traded weight for weight with gold. The World History Encyclopedia's account of the West African gold trade gives a rate far less dramatic and, on the face of it, more plausible: in the eleventh century a ninety kilogramme block of salt carried down the Niger could be worth around four hundred and fifty grammes of gold. Take the range as the range. Either way, the point stands. Two substances crossed the same sand in opposite directions, and both were treated as treasure.
What the road was carrying
The scale of the money moving along it can be measured by one document. Around the middle of the tenth century the geographer Ibn Hawqal reached Awdaghust and saw a bill of debt owed by a Sijilmasa trader resident there to a partner back in Sijilmasa. It was written for forty two thousand dinars. The episode is the subject of a study by Nehemia Levtzion in the Journal of African History. Ibn Hawqal, a man who had travelled most of the known world, said he had never seen or heard of such a sum.
The kings of Ghana understood exactly what they were sitting on. According to the World History Encyclopedia, gold dust circulated among the people, but gold nuggets belonged to the king alone. It was a display of authority, and it was also monetary policy: by holding the large pieces back, the crown controlled the supply and protected the price.
Then the gold went north and became coin. The Almoravids took Sijilmasa in the eleventh century and struck dinars there of famously high purity, drawn from the southern fields. In the Christian kingdoms of Iberia those coins were called marabotins, and later maravedis, a name that outlived the dynasty by centuries. And in 1252, when Florence struck the florin and Genoa the genovino and western Europe returned to gold coinage after generations without it, the metal behind the decision had, in large part, walked across the Sahara. Northwestern University's Block Museum states it directly: Florence's adoption of the gold standard was supported by an influx of gold from West Africa via trans-Saharan trade routes.
The coin that did not move
While all that gold was moving, one coin sat still. Constantine I introduced the gold solidus, known in Greek as the nomisma, in 312. The standard was seventy two coins to the Roman pound, which gave each coin a weight of about four and a half grammes of effectively pure gold. Britannica gives the same specification of one seventy second of a pound.
That specification did not change. Emperor Basil II was still minting to it in the 1020s, more than seven hundred years after Constantine set it. No modern currency has come close. In the sixth century the merchant Cosmas Indicopleustes wrote that every nation conducted its commerce with the Byzantine nomisma, and that it was acceptable in every place from one end of the earth to the other. He was not exaggerating for effect. Byzantine gold has been found in Russia, in Persia and in Sri Lanka. In the Islamic world it was called the bezant.
What ended it was not conquest. It was the mint. The American Numismatic Society records that Michael IV, who reigned from 1034 to 1041, took the unprecedented step of debasing the solidus. Once begun, it ran. After the defeat at Manzikert in 1071 the fineness fell from twenty four carats to eight. By the 1080s the gold in the gold coin had dropped almost to nothing. In 1092 Alexios I gave up and issued a new coin, the hyperpyron, at twenty and a half carats, and that one was worn down in its turn to eighteen, sixteen, fifteen and finally twelve, until Byzantine gold coinage stopped altogether in the middle of the fourteenth century.
The lesson on both roads
Seven hundred years of honesty, undone in about fifty years of shaving. The empire that debased the coin did not fall because of it, and it did not survive because of the coin either. But the reputation, the thing that let a Byzantine coin be spent in Sri Lanka without a scale, was gone in two generations and never came back.
The men on the desert road never had that problem. They were not carrying a promise about gold. They were carrying gold. It could be taxed, robbed or lost in the sand, but it could not be quietly reduced by an official in a distant capital. That is the difference between a metal and a monetary policy, and it is why the caravans kept coming long after the coin had stopped being worth its face.
Every fact above is linked to its published source. Chapman Gold sells antique and modern gold jewellery. Nothing here is financial advice.