Walls and bonds
How walls are built: Greek ashlar and polygonal work, the Roman facings of Vitruvius II.8 on a concrete core, and English and Flemish brick bond.
The rules it illustrates
Isodomic and pseudisodomic walls. Build walls of squared stone in regular courses with the vertical joints of each course falling over the middle of the stones below: either with all courses of one height (isodomum) or with courses of alternating heights (pseudisodomum).
Bind the faces with through-stones. In a thick wall, do not build two separate skins with loose filling between them: lay stones lengthwise into the thickness at intervals, and set single stones right through from face to face, so that the wall acts as one mass.
Break joints. Never let a vertical joint stand over another in the course below: interchange the direction of the stones, lengthwise and across the wall, so that every joint is covered and every stone rests on two.
Opus reticulatum and opus incertum. Face a concrete wall either with small irregular stones set at random (opus incertum), which is strong though not handsome, or with small square-faced stones set diagonally in a net (opus reticulatum), which is handsome but, its joints running every way, more likely to crack.
Facing and core. Build a Roman wall as two facings of brick or small stone with a core of concrete poured between them in layers; tie the facings into the core with bonding courses of large tiles laid through the whole thickness at intervals.
Pozzolana: a mortar that sets under water. Mix lime with the volcanic ash of the Bay of Naples, and the mortar will bind rubble into a solid mass that hardens even under the sea.
Where it appears in the book
In the chapters Walls and Openings, The Classical World.