Largest possible city with Roman technology

[Krases]

I based this off a similar thread in the After 1900 forum.

So I was thinking about the city of Rome and how at around 100 BC-300 AD the city sported a population of around a million people. This population was largely limited by technology and the surrounding terrain.

So my question is this: if a culture with Roman levels of technology settled anywhere in the world, how potentially large could a city become? For example, lets say a civilization as advanced as Rome pops up near where modern day Seattle is currently located. How large could a city built there become with so much in the way of resources?

This POD would have to start pretty early, but we are talking ancient times, so a POD starting in ancient Egypt would allow plenty to happen by 300 AD. The culture that advances like this doesn't have to be Roman, it just has to have such levels of technology. It could easily be a native american culture seeing as amazing things did happen in Central America or if this city is being built elsewhere, it could be in India or China or Africa.

 

[Basileus Giorgios]

There's been a thread like this in the past few weeks, I think. More than anything, a city that size is long past the age of self-sufficiency, so it must be dependent on an exceptionally fertile area to feed it, either by transporting food products from that area to the city (as with Rome up to the fifth century and Constantinople up to the seventh) or by being a capital city located in the middle of an exceptionally fertile area, as with Ctesiphon/Baghdad and, somewhat later, Cairo.

Less important but still vital factors include being located far from hostile frontiers, a climate that avoids extremes of heat and cold, and a ready supply of water for drinking and sanitation purposes.

Even with all of these factors in place, I'd suggest that it's pretty difficult to get much larger than the largest pre-modern cities were IOTL. I'd say probably 1.5 million at the absolute outside.

 

[Herzen's love-child]

The largest pre-modern cities with a technology level analogous to the Romans seemed to be in China. Luoyang in Han China in 100AD was similar in size to Rome by many estimates and Chang'an not much smaller, a little earlier. Location, resources, technology levels, relatively stable polity, organized services, & some attention to sanitation are all prerequisites for a large city in any period.
I'm going to say no larger than Rome, although historically, in the Western Hemisphere, the largest Pre-Columbian cities never got larger than approx. 250,000 tops.
One should ask why did technologically advanced societies in the Western Hemisphere tend to pop up in Meso-America as opposed to the Pacific Northwest.

 

[Krases]

They certainly 'popped up' there, but didn't the predecessors for the Romans immigrate from Greece and bring their technology with them? I picture something similar happening in the Pacific North West. I personally think that for an ancient society, Seattle would be near perfect for building a large city. Maybe not for starting a civilization, but definitely for colonization.

 

[Herzen's love-child]

They certainly 'popped up' there, but didn't the predecessors for the Romans immigrate from Greece and bring their technology with them? I picture something similar happening in the Pacific North West. I personally think that for an ancient society, Seattle would be near perfect for building a large city. Maybe not for starting a civilization, but definitely for colonization.

For a Mediterranean based culture to colonize pretty much anywhere in the Mediterranean is not a stretch because: 1.) they had the sailing traditions and 2.) the climatic environment is very similar. What they grew at home would likely grow in the vicinity of where they landed.
If you are thinking of having a Meso-American culture to colonize the Pacific Northwest, you need to have a very good reason for them to do so. Unless you are thinking of a POD that includes a gradualist approach to colonizing Northwards, it is otherwise too alien an environment for them to flourish so far afield. Pre-Columbian corn as had been bred to grow well in the Valley of Mexico would not do very well if at all in coastal Washington.
There was no tradition of long distance sailing for any of the Meso-American or S. American cultures to explore, let alone colonize, quickly.
Colonizing the Gulf coast would probably be much more realistic than the Puget Sound.

The other route-- a POD with an indigenous Puget Sound people developing a civilization that eventually develops a Roman-level technology would be interesting and I think a couple of people on this board have developed related TLs.

 

[Krases]

I think the biggest issue is going from the kind of hunter/gatherer society (though they were a bit more advanced than that) and convert over to a more agrarian society. To do this, I think they need access to a robust wheat grain that grows well in the pacific northwest.

HOW this will happen is beyond me. Plus I question the scale with which they can grow wheat without horses and oxen.