Why the new citadel walls crack, and shoring the sea front
Lime shrinkage splits the masonry; the seaward wall needs buttressing at the mountain's roots
On folio 31 recto, in red chalk, Leonardo diagnoses why the newly built citadel walls have cracked. He argues that the fissures come not from any movement of the mountain beneath them but from the walls' own shrinkage as the fresh lime dries, and warns that the seaward walls will never be stable unless they are buttressed at the roots of the mountain. A stepped section of the wall and the rock it stands on is sketched below in red chalk. Further red-chalk notes at the top of the sheet remain untranscribed here.
On this page
New walls crack from lime shrinkage, not landslip
Many new walls tied into old ones have opened cracks. Leonardo attributes this not to any collapse of the mountain on which they are founded but to the walls' own shrinkage, produced as the moisture separates from the fresh lime while it dries.
The seaward wall must be shored at the mountain's roots
He concludes that the citadel walls will never hold firm unless the part facing the sea is propped and buttressed down at the roots of the mountain. The remedy he proposes is foundation support rather than repair of the masonry itself.
Red-chalk profile of the citadel wall and rock
A stepped profile is drawn in red chalk across the lower half of the sheet, showing the wall and the rock it stands on in section. Additional red-chalk lines at the top of the sheet are not transcribed in the bundle.