In Roman times, how populated were the non-Roman parts of Europe compared to the Empire?

Turns out, it was a lot less than we thought.  This makes ample sense as densification came only with the steel plow able to break the soils.  All that meant metallurgy along the Rhine which was a later development.

It also means that those German lands were not worth taking then.

It also informs us of the type of population density encountered in the americas as well.  Every tribe established wide empty zones to protect against constant conflict.

Thus urbanized roman lands had a huge manpower advantage to work from.  They actually failed to truly optimize this, but still held off all barbarian threats until sudden climate decay uprooted the works in the fifth century..

In Roman times, how populated were the non-Roman parts of Europe compared to the Empire?

That’s a question that has kept historians busy. Karl Marx took 100,000 men, women and children as the average size for the Germanic tribes and found some fifty of them. On top of that he believed a large population of Germans existed around the Carpathian Basin (who might have been Dacians?) and added another million to their number to arrive at a population of around 6 million Germans.

Hans Delbruck was much more cautious and estimated a population density no higher than around 4 to 5 per square kilometers. For the extent of Magna Germania that would yield a total population of around 2.3 million.

A further complicating factor is that Roman sources suggest parts of Germania weren’t inhabited. As a result of the frequent wars some of the larger tribes allegedly kept depopulated regions of no man’s land between them. In other words the population depended not only on soil fertility and existing agricultural techniques but also ‘social carrying capacity’ which was the density at which various political groupings could be accommodated. The frequent migrations outside of the Roman Empire are also supposed to have only been possible in a sparsely populated or partially empty landscape.

Archaeology hasn’t been able to tell us everything but it does shed some light on the matter. For one ancient authors seem to have been right when they mentioned no man’s land. Entire areas of Europe outside the Roman border seem to have been uninhabited. Regions with archaeological finds alternative with empty strips of land. There also appears to be something of a West-East gradient. Settlements are bigger and become permanent earlier in the western regions than they did in the eastern regions.

A recent study suggests broadly speaking that the region between the Rhine and the Vistula held between 1.6 to 2.4 million. That would mean we’re looking at around 3 to 5 persons per square kilometers.

For comparison Roman Italy in AD 165 is believed to have had a population density of 27,4 per square km giving it a total population of nearly 8.5 million. The entirety of the European part of the empire averaged around 14,4 persons per square km yielding a population of 36.9 million. Estimates for the entire Roman empire at this demographic peak are around 65 to 75 million.

Magna Germania wasn’t the only part of Europe not controlled by Romans. Towards the east the region known as Scythia or Sarmatia was inhabited by Finno-Ugeric, Iranian and potentially proto-Slavic speakers. From what I gather this region and Scandinavia were even more sparsely inhabited than Germania. I haven’t been able to track down estimates for these regions but if I had to make a guess i’d say we’re looking at no more than 2 to 4 million in all the rest.

In other words I reckon the population living outside of the Roman Empire was in the vicinity of 4 to 6 million people. Combined with the figure of 36.9 million people living in European Rome we arrive at a total European population of around 40,9 to 42,9 million people.

This would mean that around 86 to 91 per cent of Europeans living at the time lived inside the Roman Empire. Perhaps somewhat shocking to modern Europeans who tend to see the Roman Empire as more of a Mediterranean thing.

Perhaps its also good to put these numbers into perspective.

Estimates for the 7th century give a total European population as low as 18 million which suggests the population of Europe had halved since its Roman peak. Though note that this loss must have been proportionally more severe in the Roman occupied areas.