Update

To help with the reconstruction of the Siege era design of Bishops gate I've been looking at a variety of sources and focusing on 16th/17th era fortification design - from this I've created a 3d mock up to use as reference for the sketched renderings  -  I need to confirm with Mark Lusby & his associates the accuracy - below fig a. is one of the widely used images pertaining to the siege which I have been notified is inaccuate so I've been looking at proxy fortified settlements of the era and contemporary renditions from the period such in fig b.

 

fig a.

 fig b.