The standard consular army of the Romans during the Polybian era consisted of 2 legions and 2 alea's of each 5000 men. During emergencies, the two conculs would join armies, resulting in troop totals of 40,000 men or higher. However, the R:TW engine is limited to 20 units per army, and 260 men + 3 officers per unit, so it cannot be used to represent these numbers.

Similarly, population can be modded but unfortunatly the associated squalor penalty cannot. A city with a million inhabitants would have such a high squalor level that it would be impossible to keep under control (and population would decrease rapidly as well). Of course, since almost the entire population count of a city can be recruited, I guess it represents households rather than actual inhabitants.