I thought that the DMG numbers as is don´t work out so well. At least that´s what I heard.
These are numbers for a medieval setting btw, Eyros is leaned on the roman empire with sophisticated infrastructure. In that time cities were bigger.
My personal preference would be at least a population of 10 million for the whole of Eyros.
Some food for thought: Isf you don´t want to read it all, just jump to the summary.
I use this sites as points of reference
-CIA Worldbook of Facts:
http://www.cia.gov/cia/publications/factbook/geos/ca.html (demographic, geographic, political atlas)
-Historical population date of the roman empire
http://www.tulane.edu/~august/H303/handouts/Population.htm
Eyros
Proposed population of 1,000,000
Land Size : 1,500,000 square miles/ 3,840,000 sq km
Population density: 0,26 people per sq km (I use these as the atlas is only using km)
Of course Eyros could not be compared to modern countries and their populations, but it´s nice to have point of reference to get better grasp of numbers thrown around.
For comparison I took the lands with the largest ratio of landsize to population I know:
Canada
Population: 32,507,874
Land Size: 9,093,507 sq km
Pop. Density: 3,57 ppl/sq km
Australia
Population: 19,913,144
Land Size: 7,617,930 sq km
Pop. Density: 2,59 ppl/sq km
Tried Russia, too, they were around 8,4 ppl/sq km
So Eyros population density is ten times lower than that of Australia
Of course Eyros has several factors that speak for a lower pop density.
-Not a modern nation with all it implies.
-Magic threats
-Sometimes really harsh winters
Comparison to the Roman Empire
As the general mood of Eyros was modeled after the roman empire I now compare Eyros to the Empire. I haven´t found exact size but it was about the size of the U.S.
The Europen Union includes the bulk of the former western roman empire, without the northwestern african parts of course, but including nations outside the former empire, like Finland, Poland, and so on. Eyros is nearly as large as the European Union.
The population of the western empire was around 22 million people, with 1 million guys living in Rome alone.
That´s a possible maximum but Eyros probably has a lower population:
Reasons:
Magical Threats
Races with lower birth rate
Lower urbanization as far as we established here
Harsher climate sometimes
Less fertile area with less rivers (think so)
Eyros is a lilttle smaller than the western roman empire (my estimate)
Eyros probably has a better healthcare with divine magic available.
To take this into account I removed the two provinces with the highest numbers:
Gaul & Rhineland: 5,000,000
Italy : 6,000,000
So that would leave 11,000,000 people.
Eyrdeyn should be smaller than Rome of course, perhaps it´s not even the largest city. The city is built on a volcano with limited space, who erupts sometimes, the empire is smaller, has a lower population density and urbanization seems to be lower than compared to the Roman Empire.
I would say Eyrdeyn could be somewhere around 200,000 to 600,000 people.
SUMMARY and Conclusion:
Eyros with a population of 1,000,000 people has a ten times lower population density than Australia, the roman empire that Eyros is modeled upon had 22 million people in its western parts, an area that has a comparable size to the Dominion. There are several negative influences that would indicate a lower number, so a number of 11,000,000 individuals should be appropriate if we want to keep realistic figures.
We could still use the 1,000,000 individuals figure but without a lot of hand waving such a low number could not support an empire modeled after the roman empire. The population would indicate a more feudal system with lots of smaller lords with a lot autonomy, a weak central authority, a weak infrastructure, low mobility and no standing army as there are simply not enough people to support one. The great houses are probably not able to enforce a central authority and most power would be on the lesser nobles.
The number of soldiers are 20000 if we go with Arkhandus post. Thats 4 legions protecting the empire. For comparison the roman empire needed up to 35 legions plus auxilliary troops to defend its territory.