Just queing peasants units can improve loyalty and decrease squalor. Those peasants can then be moved to cities you depopulated, where they join the general population once you disband them.

This works very well on large unit size, and I presume on huge. One large-unit peasant has 120 men.

The mathematics still need figuring out. There is a threshold. Some turns, you can que one or two peasants and see immediate effects. Others, you can que five or six before seeing a measurable change.

If you click on the full settlment display while you have the recruitment screen up, you can see the effects on loyalty and squalor while you que up.

This is an extremely powerful tool if you conquer Greece and occupy the cities, then take over Asia Minor, wiping out populations all the way. These settlers also allowed me to transform Crete from a barbarian backwater into a prosperous city with 2,000 citizens quickly, just with peasants and nothing but peasants from Greece.

As the Brutii, even the peasants get the faction's Temple of Mars bonuses. It was certainly enough to make the conquest of Crete effortless.

I need to whip up on Thrace and get Byzantium. Then a steady flow of "settlers" can cross Asia Minor with very little ship movement.

Also, the combination of Colesseums with frequent games to offset high taxes can really keep the population under control while settlers can reduce squalor. A city of 12,000 with a population growth of 1 percent produces 120 new citizens, after all.