What to you are the essential things for running a game in a post fallen roman empire? Do you have a list of things that are needed to give it a certain feel?
Technically, that's "late antiquity" or even more colloquially "the Dark Ages", which has a completely different feel to classical antiquity several centuries before.
There are some basic things to do, like changing the standard equipment list - plate armour and things like two-handed swords don't exist. Are you going for a straight historical game, or just something vaguely inspired by history?
More vaguely inspired by history.
- Lamellar, banded and plate armor are only available in Class I markets (e.g. the equivalent of Byzantium).
- Two-handed swords and crossbows are not available in any markets.
- Books are considerably more expensive and valuable. They cost twice as much in Class I markets, three times in Class II, four times in Class III, five times in Class IV, six times in Class V, and are absolutely unavailable in Class VI.
- Reduce the range of all trade routes between settlements by half (land) and one-quarter (water). Trade has largely collapsed. Demand modifiers will be sharply disparate between major settlements, which no longer are able to trade with each other.
- Make heavy use of Special Treasure in lieu of coin treasure. Coin was increasingly scarce and goods were used in barter instead.
- Double the number of mercenaries.
This could almost be an AXIOMS article - adapting ACKSonomics for different cultural settings.