Iron Portcullises, Machicolations, and Low Entrances
Fireproof iron grilles, furrow-like machicolations, and hidden reversed gates for a keep
The right page details gate defences and the castellan's control of his own fortress. Portcullises should be of iron and drop easily, with long narrow machicolations above shaped like furrows so defenders can strike along a crowd bringing a beam to lever up a burnt, red-hot grille, though a crooked approach is judged better still. Leonardo again urges that entrances lie as low as possible, be made by reversed ways, and be screened by a solid ravelin against the bombards, and repeats that the castellan must guard above all against his own household. A small pen sketch at the lower left, marked a, shows a cylindrical tower with its gate mechanism.
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Iron portcullises that drop easily
The portcullises before or within the fortress doors should always be of iron and descend with ease. Their fireproof metal is meant to survive an attempt to burn the gate. The sketch marked a at the lower left shows such a grille within a round tower.
Furrow-shaped machicolations and a crooked approach
Above the gate, long narrow machicolations like furrows let defenders strike down the length of a crowd carrying the beam with which they would lever the red-hot grille up and cast it down once the door had burned. Better still, Leonardo notes, is to make the approach crooked so that no such beam can be brought to bear.
Low reversed entrances and guarding against the household
Fortress entrances should sit as low as possible, be reached by reversed ways, and be shielded from the bombards by a solid ravelin in front. The castellan's chief and most diligent guard is against his own trusted men and household, who have the greatest opportunity for betrayal; the weakest point of the site should be made the strongest with towers and ravelin.