how do i convert a minor/large city to a castle/fortress

[The Source]

tite^^^^

[thursgun]

I don't remember if large cities can convert, but minor cities sure can. Go to the construction panel and choose to 'build' the 'convert to castle'.

[Spartan90]

You can't convert large cities to castles, sorry. If that was the case, people would take extreme advantage of this, as it's 10x easier to get a large city than it is to get a Fortress / Citadel.

[Exarch]

once those brick walls are built, u cant change those cities to castles no more

[nderim78]

Convert to 3 and 4 was missing from the export_descr_buildings.txt. I know, over a decade, but better late than never. After playing a ton of times and corrupting my files, I finally got something:

[Gigantus]

I think the game idea was that it was simply illogical\impractical to convert anything larger then a city into a fortified (castle) settlement, given the size of such a settlement. Correspondingly you can only convert a castle settlement back to level 2 max, regardless of castle level. Having a citadel turn into a huge settlement would be kinda nuts considering the size and population discrepancy.

But a nice find nevertheless