Fortress Design: Concealed Sally-Ports and Defenses
A fortress with round bastion towers; notes on secret passages and obtuse defensive angles
A large drawing shows a fortress or castle in perspective, dominated by massive round bastion towers, gates and stepped walls. Two columns of notes set out rules for its defense: a concealed walled sally-port thin enough to be removed from inside and wide enough for a man to crawl through, kept remote from the known relief passages, with false ones built into the massive walls. Further rules govern defensive angles (only strongly obtuse ones), tower scarps, flanking gun-ports, and the housing of the paid garrison, recalling the betrayal of Simon Arrigoni and precautions against enemy mining.
On this page
A concealed, removable walled sally-port
A walled stone entrance is to match the other large stones but be thin, so that it can easily be removed from within, and as wide as a man can be to crawl in or out lying down. It should lie as far as possible from the known relief passages, while false relief passages are built into the massive walls.
Tower scarps, flanking gun-ports and garrison quarters
The scarps of the towers over the fortress corners are not to be round, so that the enemy cannot safely reach the cut-off between the gun-ports firing along the flanking walls. The paid soldiers must be able to be fired on day and night by the castellan, sleeping in thin-board dwellings under straight porticoes with gun-ports in front, a lesson drawn from false reliefs such as the betrayal of Simon Arrigoni.
Only strongly obtuse defensive angles
No angle is to be made in the defenses where artillery can strike unless it is strongly obtuse, because a sharp angle is what begins the ruin of the walls. As much solid mass should be built into the scarps of the first wall enclosures as the enemy needs for driving underground mines.
Fortress with round bastion towers
The sheet is filled by a perspective view of a fortified structure with cylindrical bastion towers, arched gates, sloping scarped bases and stepped ramparts, the built form to which the defensive notes apply.