The basic principle for achieving this is very simple: we convert our castles into cities in order to increase our population growth!

However, there's a little caveat when it comes to doing this - a relatively obscure mechanic that I'm sure many people aren't aware of. That included me until I managed to stumble across it while doing some research.

Simply put anything from a minor city and upwards (minor city, large city, huge city etc.) can no longer be converted into a castle. It's stuck as a city for the rest of the game.

What this means in practice is that we need to grow our population to 4500 (the requirement for upgrading to a fortress) without upgrading our settlements past the level of a large town!

The actual population count doesn't matter when determining a settlement's 'convertability', only the actual settlement level!

In summary, do NOT upgrade your cities past the level of 'Large Town' if you have ANY intention of ever converting it into a castle in the future. The option will no longer be available.

Now, here are a few ways to increase your population growth%.

1.) Lowering taxes. Each level of lowered taxes will increase your growth by 0.5%.

2.) Small church. Building a small church (1st level of building) for 800 florins will increase growth by 0.5%.

3.) Brothel. Building a brothel for 800 florins will increase growth by 0.5%.

3.) Farms. Each farm upgrade will increase growth by 0.5%.

4.) Town hall. Building a town hall for 600 florins will increase growth by 0.5%.

5.) Sometimes trade buildings (ports, grain exchange etc.) will increase population growth by 0.5%. Open settlement details tab when constructing the building to see if it (a port/ grain exchange) will increase your population growth.

6.) The BEST way to increase population growth in a settlement is to have a high chivalry governor stationed there. Every level in chivalry will increase the population growth by 0.5%, which is a tremendous bonus. At a maximum chivalry of 10, your governor will add 5% population growth to the settlement! Amazing!

It's important to note that squalor will also increase as your population growth increases. This means that more population growth beyond a certain % will have diminishing returns.

Do be aware that some buildings will not survive the conversion from town to castle.

From the +growth% buildings I listed earlier, the brothel, town hall and grain exchange will not survive the conversion.

If you are interested in building them purely for more growth, then demolish them before you convert to get some cash back.

I hope this guide has been helpful. Have fun steamrolling the map with your knight rush.

Deus Vult!