The Four Books of Architecture

BOOK FIRST###

E: Courses of small bricks original: "quadrellini" that bind the entire wall together.
F: The middle part of the wall, made of rubble masonry original: "cementi" – referring to a core of small stones and mortar placed between the horizontal courses and the exterior bricks.

Rubble walls shall be constructed so that at least every two feet there are three courses of baked stone pietra cotta: bricks or terracotta, and let these bricks be arranged in the manner described above. In Piedmont, the walls of Turin are made in this way; they are constructed from river pebbles original: "cuocoli di fiume" that have all been split in the middle. These pebbles are placed with the split side facing outward, which results in a very straight and polished finish. The walls of the Arena of Verona are also made of rubble masonry, and every three feet there are three courses of bricks; many other ancient buildings are constructed in this same fashion, as can be seen in my books on Antiquity.

G: Rubble masonry, or river pebbles.
H: Courses of bricks that bind the entire wall together.

Those walls made of stones with unequal angles and sides were called "uncertain stones" This refers to opus incertum or polygonal masonry, where irregular stones are fitted together like a puzzle. To build these walls, the masons used a lead square A flexible measuring tool that could be bent to match the specific angle of a gap, allowing the mason to shape a stone to fit perfectly which, when bent to fit the space where the stone was to be placed, helped them in shaping it. They did this so the stones would join together perfectly, and to avoid having to repeatedly test whether the stone fit well in its designated spot. Walls built in this manner can be seen at Preneste Modern-day Palestrina, famous for the massive terraces of the Sanctuary of Fortuna Primigenia, and ancient roads are also paved in this way.

I: Uncertain stones.