Say there is a floating city that rests high in the air, it has the area of around New York City and has massive hydrogen tanks under it to keep it afloat, (I am aware the physics of this is impossible, but this takes place in a fantasy setting so I am not concerned), and the residences have air filters to counteract the altitude. Now say that this city is at war with another city, and one of them launches an attack. How would this go down, more specifically, how would this enemy city besiege another? This would not just mean destroying the tanks under the city as it is necessary for my story that these people board it and rescue a person inside the main palace whilst doing so.
City Structure This city rests on a platform of thick concrete in a perfect circle, and as I said has massive tanks of hydrogen keeping it afloat. The building as made of wood as to not weigh down the structure. There is a main structure which is a sort of palace located in the middle, however, it is highly defended. The city also stays in one spot and does not drift. This city grows crops inside the city walls as well as harvests condensed water from clouds, so cutting off supplies is not an option.
City Defences See question:Siege defences for a floating city
General airship design These airships have the hull of a regular 12th-century medieval liner. This liner has two leather horizontal gliders on either side (outriggers) responsible for keeping the airship afloat. These airships can also go above and below, as they can leak and add hydrogen to the tanks. (Note that you can change design structure as long as you ask in the comments and I approve first).
Notes Has technology equivalent to that of Imperial China. Is follow-up to:Siege defences for a floating city