You have a little under four years to breach the walls of the Pig's castle and put all the defenders to the sword. To be exact,the Pig will arrive in September 1223 and if there's any soldier left alive in the castle at that time...you're history.
The game suggests storming the gatehouse and battering it down. I tried this approach several times and got nowhere. On my first attempt I'd breached the inner court by the time the Pig showed up, on later occasions I managed to get most, if not all of my troops massacred. It was time for a different tactic.
The beta game had a moat that did not extend all the way on the west side of the castle. This spot was easily breached, but the full version has a moat. I decided to try anyway.
All archers, there's two groups, were gathered and set to cleaning the western towers of archers and crossbowmen. Meanwhile all remaining troops were brought westwards. Once the walls were cleaned a few dozen spearmen were dispatched to fill in the moat. As soon as it was filled in (November 1221) I sent in 4 tunnelers one after the other. They were set up in a staggered pattern one after the other and quickly breached the wall, a breach some 3 tiles wide. The breach was used to send in several squads of macemen and spearmen to clean out the archers remaining in the inner courtyard, while my remaining archers and my crossbowmen took out the defenses around the keep. As soon as the inner keep was cleaned out the archers were set to do the same in the outer courtyard.