Twin fortresses for two castellans: shared gates and walls
Round keeps 100 feet apart, double curtain walls, moats and chained entrances neither castellan controls alone
Folio 86r sets out several schemes for twin fortresses that could be held jointly by two castellans. Leonardo describes two round keeps 100 feet apart linked by curved double walls with guardrooms in their cavities, a shared entrance whose chain each castellan pulls so that neither can admit anyone alone, and further pairs of towers joined by double walls, moats and assigned bridges. The emphasis throughout is on mutual control of the gates and on dividing the interior into fitting rooms.
On this page
Two round keeps joined by circular walls
Two round fortresses are set 100 feet apart, from which run two curved, reversed circular walls with the entrance of one castellan passing through the keep of the other. In the hollows of the doubled walls are placed the rooms for the guards.
A shared entrance controlled by both castellans
At the common entrance of two joined keeps the chain on one side is pulled by one castellan and that on the other by the other, so that neither can admit anyone without the other. Each must have a covered passage from his tower to the chain of the gate or portcullis.
Twin towers, double walls, moats and bridges
A further scheme sets two towers 100 feet apart with internal divisions, joined by a double wall; another places two keeps 60 feet apart, joined below at the entrance and separated above by walls and moats, with two opposite entrances and bridges assigned to each castellan, the rooms laid out along the diameter.