[MaxWilson]

What fort are you besieging? If it's a Crystal Citadel or something (1200 defense) you can either leave a large but cheap-quality sieging force outside of it while your real units keep conquering other provinces, or forge items like the Gate Cleaver (requires Earth-3) and the aforementioned Wineskin (Nature-1) and Cauldron of Plenty (Nature-3) to provide siege bonuses and/or allow more besiegers.

Call of the Winds provides a cheap addition to your sieging forces. Some people like it better than Wall Shakers; I think it's easy for all the hawks to die, but on the other hand zero-upkeep flying commanders can be really nice as gem couriers and troop shuttlers.

-Max