Sometimes you start wondering how big a reasonably sized army would be for one of the world’s cities, so you have to do research on population sizes in Renaissance Europe. You set an arbitrary but realistic number, then you figure out the proportion of men to women. Then you take that and get a number of military-age men. Of course, not all of these could be in the army at one time for various reasons so you have to find out what percentage of a population is usually in a standing army. Then you do that for each city. But then there are many times more people living in rural areas under lesser lords than in cities, so you account for that too. Then you project factors that affect population, like disease, war, and natural growth through birth, and that messes with your military numbers over time.
Do this a bunch and you’ll end up with lots of useful numbers that help you not make silly oversights when talking about these wars, like saying that the lord of a city with 20,000 people was able to muster 50,000 men.
In the end, you come to the conclusion that Heilicon (including surrounding farmland also under the banner of Lord Alfonse Mennish) had 39,622 inhabitants before it was destroyed. In contrast, Lord Leopold Ment’s armies marched with over 20,000 soldiers, nearly half of which went to Heilicon. And this is how you go overboard on details that most people won’t care about.