To Borgia

Illustrissimo Signor mio,

I write from Cesena, where the rain has not ceased these eleven days and the clay beneath the eastern rampart has begun to slide. I have measured the displacement with a plumb line and a cord fixed to the merlon at the northeast angle: the wall has settled four dita since the last moon, and the crack that was a hair’s breadth in March is now wide enough to pass a thumb. This is not the work of age. It is the work of water.

The foundation was laid upon gravel, as I specified in the drawing I sent you in February — the one with the cross-section showing the rubble core and the outer face of brick set upon a footing of cut stone two braccia below the grade. But the gravel bed was not drained. The contractor, whose name I have written in my notebook and will not repeat here until I have proof of his negligence, allowed the trench to fill before the first course was set. The water has nowhere to go. It lifts. It pushes. The wall follows.

I have ordered a trench cut behind the rampart, two braccia deep, with a slight fall toward the canal, and I have directed that it be filled with broken tile and river gravel, packed in layers, so that the water may drain away from the foundation rather than pool beneath it. This will cost perhaps forty ducats in labor and material. It should be done within a fortnight if the rain permits. If the rain does not permit, we must wait, and the wall will settle further, and the cost will rise.

The canal itself — the one I surveyed last autumn, running from the Savio toward the town — is in better condition than I expected. The bed is sound where we lined it with puddled clay, but at the point where it passes beneath the road to Forlì, the embankment on the south side has been cut by carts. Someone has driven heavy loads across the towpath and broken the clay seal. Water is seeping through. I have marked the spot with a stake. It must be repaired before the autumn rains, or the road will soften and the artillery cannot pass.

I have also examined the placement of the two culverins on the eastern wall. They are positioned as I drew them — one at the northeast angle, one at the midpoint — but the platform for the midpoint gun is too narrow. The recoil will carry the carriage into the parapet after three or four shots unless the platform is widened by at least one braccia on the inner side. I have spoken to the master of the artillery, a man from Bologna who understands his guns but not his masonry. He insists the platform is sufficient. He is wrong. I have drawn the correction and left it with the castellan.

The soul of a fortification is not in the height of its walls but in the direction of its drains. A wall that stands dry will outlast a wall that stands proud. I have seen this in Milan, in Naples, in places I will not name. Water is the enemy that never sleeps.

I remain in Cesena until the work is done, or until you send me elsewhere. My hand is steady enough for the compass, if not for the brush. The maps I promised for the Imola approaches are nearly finished. I will send them when the ink is dry and the roads are passable.

Vostro servitore, Leonardo

Written this day, the fifteenth of June, in the year of our Lord fifteen hundred and twenty-six, at Cesena, by my own hand, which trembles but does not yet fail.