In the original grand campaign there were a few sieges that took place. It was done on battle mode, 1 life per person, each round went on for a very long time but it was incredibly fun.
Having experienced defending and attacking a few times, both require a lot of communication. Back then it was done with Generals with whispers list and usually with the officers of each regiment communicating with each other via whispers too.
Organised sieges are my most fond memory of MM and I would love for it to return, with Generals and whisper lists preferably.
Edit: A video made by own of the 95th members for a GC siege event, not exactly serious.