The Castellan's Secret Passages and a Hexagonal Fort
Guarding against treachery within, and a hexagon with a central triangular tower
The left page treats the security of a fortress against betrayal from within. Secret caves and subterranean ways should let the castellan move through every level yet keep his own dwelling unreachable, and with portcullises and floodgates he can imprison plotters and control the main and relief gates; Leonardo warns that trusted insiders are more dangerous than the enemy outside and that portcullises and drawbridges must be propped to prevent their being shut in. A second note lays out a fortress bombardable from only one side as a hexagon with its solid angle to the weak part, two rear towers, and a central triangular tower two-thirds solid, entered by drawbridge and portcullis and ringed by a ditch. A pen diagram shows the hexagon with its inscribed triangular tower.
On this page
Secret ways that keep the castellan safe from his own men
Secret caves and subterranean passages let the castellan traverse the whole fortress above, in the middle, and below, while none of them reaches his dwelling without his leave. With portcullises and floodgates he can imprison in their rooms any of his men who plot against him, and open or shut the main gate and the relief road. Leonardo insists this inner guard matters more than defence against the enemy shut outside.
Propping portcullises and drawbridges from below
Those who fear being harmed through the portcullises and drawbridges should shore them from below, so new devices are needed. Whoever would hold a portcullis props it against every direction in which it might move, so that he is not shut in by it.
A hexagonal fort with a central triangular tower
For a site bombardable from one place only, the circuit is drawn as a hexagon turning a solid angle to the weakest part, with two towers set back at the neighbouring angles and a triangular tower between them, one angle to the weak side and two-thirds of it massive. The tower's door, on the opposite side, has a drawbridge and portcullis, and a ditch rings the whole, most useful here because the ground is low.
Diagram of the hexagon and inscribed triangle
A pen sketch at the upper left shows a hexagonal enclosure with a triangular tower drawn inside it, matching the described plan. Small circles at the angles mark the flanking towers.