How to Siege a Castle for Fun and Profit
The first step is to raise an army. Rome wasn't built in a day, you know, and neither is an army. To get all the men together (you need 16,000 at least, though you'll wish you had a million), supplies, training, equipment, will take at least the winter and at most 2 years (unless your army is especially daft).
Before you begin, ask yourself the following questions:
1. What is the terrain? Is the castle on a large field? Then you probably want a large army with some decent cavalry to mop up any escapees. Is the castle bordered by the sea? Use some ships to back up your land army. Is it in the mountains? Close off the roads and use infantry almost exclusively. Is it on an island? Naval blockade. Pick the right force for the right job.
2. Why are you attacking the castle? Do you want it for yourself? You should probably surround it and starve out the current residents. Pack plenty of food, because you can be certain that they will. Is it in the way? Use siege engines to knock it down. Do you want to make an example? Find a way in and slaughter everyone. If you don't know why you are attacking, go home.
3. Consider your enemy. Does he have allies? Is his army fielded? Does he possess a superior number? Better technology? Is he more handsome? Take all of these factors into account before you start.
4. What are the consequences? Who would retaliate? Would your major religious leader or secular ruler be upset? What happens if you lose?
If you have decided, after asking yourself these questions, that you wish to go through with this, congratulations! You are on your way to making war. Organize your men, discuss your plan with your subordinates. Before you go, check your "Handy Checklist of Sieging":
Food for at least a year
Personal Equiment and Effects
Did you use the bathroom?
Is your fireplace still on?
Small siege engines (ballistae, small rams)
If all of these are checked, go ahead.
Starting Your Siege
Okay, you've bottled your enemy inside his castle. Ask for his surrender. Either he'll give in, or tell you to go to Hell.