Regarding cities and Castles

[YuriVII]

Simple problem. I am more or less in the year 1250 and I cannot advance beyond Large City or Stone Castle. Population for Castle hovers at around 5000 while city hovers around 10,000. There is no option to expand the settlements.

Also, everyone but me seems to be stuck with wooden castles.

[anaztazioch]

Its era restrictions. You cant go to Sone Castle untill scrolling message will say that it is about time when medieval europe started using stone castles.

[YuriVII]

I can get to Stone Castle, just going to "fortress" is the problem here.

[apw2]

When you play you should notice little scrolls on the left popping up and giving you a message about a new era "chain mail discovered" or something, there will be lots of them. With each one of these a new era has been entered and something new can be built/recruited. There will be one for stone castles, another for fortresses, there is one for blacksmiths etc...
Personally, i removed most of them since i didn't like having my entire infantry army of weak soldiers (although the best available) routed and killed by 3 rebel generals in the same army.