The urban population of Europe began to decline even before the fall of Rome. The city of Rome had a million inhabitants in the 1st century ce. By the time barbarians crossed the Rubicon River on their way to plunder Rome the city had lost over half its population. At the end of the 14th century Rome had less than 20,000 people.
Many urban sites in northern Europe were abandoned during the Dark Ages. Others remained hollow shells, the population largely depleted. Basic supplies were drawn from the surrounding countryside.
Trade over long distances was largely confined to luxury goods, including slaves. This was conducted by foreigners, mainly Jews and Syrians, for the benefit of both secular and religious men of means.