I have started a campaign on "prince" difficulty, including messengers and fantasy world.
I had no big problem getting to the second map, but as soon as I am there, there is a message about ogres being sighted, and a few months later, they club my castle to little pieces. Now i barely have the time to build two towers and three wall segments before they arrive, and with high wages for my warriors, i get to a force of 100 archers and 100 infantry maximum. Plus the ogres seem quite strong, meaning that one of them can easily take on more than one of my men. Any idea what to do to build up my defenses on time?
Troop strenght depends on castle size, correct?

Thank you, I got that resolved. I had to set game speed to 'laboured', then quickly design as much as possible of the castle. Then I would raise the army's wages to maximum and set hire up to 500 men of each kind. by the time the ogres attacked, there were enough soldiers to stop them. Also helpful: If the foundations of the unbuilt castle are in the enemy's way, he will first smash those while still getting shot at by archers.