Adventuring in the Partially Abandoned City of Khromarium

During the Roman Empire, the city of Rome reached a peak population of around a million people. However during the Middle Ages its population dropped to the tens of thousands of people. One source I've seen says 20,000, another 50,000 - in any case, a monumental decline). The Coliseum at one point served as a landfill.

I've been thinking about this as I prep for a campaign in Hyperborea. There, the largest city is Khromarium, with a population of around 30,000. However, a reading of the Referee's Manual for AS&SH shows how much Khromarium has fallen from its peak. Depopulated twice - once upon the advent of the Ashen Worm, with Khromarium buried under ice. The second time, in more recent history, in the aftermath of the Green Death.

Having once been the capital of the Hyperborean Kingdom - for "untold millennia" I picture it also having once had a population in excess of a million. Reduced to 30,000, that is perhaps 3% of its former glory. Page 208 of the Referee's Manual gives us a nice mental picture:

Presently Khromarium is a dismal, seedy place, choked by the smoke of its factories. Some 30,000 or more individuals reside in the city, but as poverty and homelessness are alarmingly high, reckoning an accurate census is difficult. The bulk of the populace dwells at the south side of the city, close to the harbour. Twisting towers of black gneiss dominate the north side of Khromarium; this is called the “Old City”, where large groups live on the streets in tents and ramshackle dwellings, afraid to enter the towers (which are commonly held to be haunted). 

From coast to coast, like a great semicircle, Khromarium is walled in, protecting it from the beasts and horrors of the Lug Wasteland and the savage barbarian nations farther north. All manner of siege engines are mounted on these walls, and where the walls and towers meet the sea, these may be unleashed on enemy vessels.

I visualize almost two cities. A dense cluster close to the harbour. Perhaps even with its own walls - or at the very least carefully patrolled. And a much larger city with ruins, haunted towers, creepy monsters, wandering brigands, etc. It's almost like the rest of the city is its own wilderness, a bit like the old RuneQuest setting of Pavis and Big Rubble. Yet we have the suggestion that the outer wall is patrolled to protect it from the barbarians to the north. It is understandable that they'd not withdraw to the core - that would allow the barbarians to get a foothold in the city proper.

As a boy originally from New York City, I picture it as if the population of Manhattan has been reduced to a tiny fraction of its former self and confined to Battery Park. The rest of the city is for the most part abandoned but the entrances - the bridges and the like - are still carefully guarded.

This is an area ripe for adventure. Its size is comparable to that of Greyhawk - the 1st edition Gazeteer gave it a population of 53,000 - bigger than Khromarium, though not by orders of magnitude (and the population estimate for Khromarium is very rough). This makes the city a good place for urban adventures like those seen in Lankhmar. But for dungeon crawls, there's no need for a long journey in the wilderness - there's plenty of ruins to explore within the Old City. That's not to say adventure in the wider world isn't a possibility, but it does give the characters a nearby home base for their dungeon excursions.

What I'm doing for my own campaign prep is working on a tower and dungeon complex below. I'm not picturing a massive megadungeon but one with several levels - enough to get our adventurers up a few levels. It's got me thinking about the dungeon ecology - who is in the ruined tower, who is in the upper levels of the dungeon, who is in the lower levels, etc.? Do they know about each other? Do they fear each other? Who might move into the upper levels if the characters clear it out?