To Borgia

Illustrissimo Signor mio,

The guns at San Leo stand too high on the curtain wall. The parapet catches the recoil and the masonry cracks. I measured the thickness of the merlons yesterday — they are 4 braccia where they should be 6. The stone is good but the angle is wrong. The artillery must sit lower, behind a sloped earthen ramp so the shot does not shear the coping when it fires.

Send me the masons with their picks and the engineers with their levels. We will cut a new embrasure at 12 degrees downward. The embrasure will be 3 braccia wide, notched so the cannon’s trail does not bind when it is run back. The embrasure’s sill will slope inward 2 palmi so rain does not pool inside the embrasure and rot the wood of the carriage.

Cost: 12 ducati for the masons, 3 ducati for the timber to shore the embrasure while it is cut. The work will take 8 days if the weather holds.

I have sketched the profile on the last page of this letter. The diagram shows the new embrasure in red.

Valete,

— Leonardo