North and East, I say! Mainly because of the Picts and Parthians. So, you could expand it to Scotland, maybe some of Scandinavia, and central Asia, say around Alexander's conquests.

Of course, this would leave you with a large corner of the Russian steppe that might be unihabited and barren...

Unfortunately, this is all academic right now...

I mean, wth was CA thinking?!?! "Oh, all they will want to mod is the skins for units. They won't want to add more than 30 factions, more than 300 units, or add models, change models, or change the campaign map even a tiny little bit, or make a mod without the senate. And just to make sure, we'll make it very hard and tedious to do any of these things and not give any support whatsoever."?!?!?!

Not that I'm blaming the individual employees, for we all know that the god G'Nitekram is cruel and heartless, not to mention moronic...

Most moddable of the series-if all you want to do is change the colors!!
/rant

Crazed Rabbit