Does anyone have any tips for assaulting fortified cities?

I was playing in an early British campaign, attacking one of the pirate bases in the Caribbean. However, I noticed too late it was fortified. The idea of going through the meat grinder of assaulting it was too horrible, so I reloaded and starved them out. I suspect that was the best decision, but has anyone got any tips for how to manually fight out a siege assault?

I am familiar with doing it in MTW2, but ETW lacks the siege towers, ladders and rams etc that I would use there. How do sieges work? Can your men scale walls as in STW2? The walls seem impregnable to artillery, although the gates are not.