The Da Vinci Notebooks at sacred-texts.com
The way to give stability to the arch is to fill the spandrils with good masonry up to the level of its summit.
An arch of small curve is safe in itself, but if it be heavily charged, it is necessary to strengthen the flanks well. An arch of a very large curve is weak in itself, and stronger if it be charged, and will do little harm to its abutments, and its places of giving way are o p.
88:404 : Inside the large figure on the righi is the note: Da pesare la forza dell' archo.