Marshes that are stagnant and have no outlets either by rivers or ditches, like the Pomptine marshes, merely putrefy as they stand, emitting heavy, unhealthy vapors. A case of a town built in such a spot was Old Salpia in Apulia ... Year after year there was sickness, until finally the suffering inhabitants came with a public petition to Marcus Hostilius and got him to agree to seek and find them a proper place to which to remove their city.

Leave a cavity behind the [wall] facings, and on the inside build walls two feet thick, made of red dimension stone or burnt brick or lava in courses, and then bind them to the fronts by means of iron clamps and lead. The beds and builds, all settling equally and bonded at the joints, will not let the work bulge out, nor allow the fall of the face walls which have been tightly fastened together.

Bricks should be made in Spring or Autumn so that they may dry uniformly.

The oak has not the efficacy of the fir, nor the cypress that of the elm.

Trees which grow in places facing the course of the sun are not of porous fiber but are solid, being drained by the dryness... The trees in sunny neighborhoods, therefore, being solidified by the compact texture of their fiber, and not being porous from moisture, are very useful, so far as durability goes, when they are hewn into timber. The lowland firs, being conveyed from sunny places, are better than those highland firs, which are brought here from shady places.

Some springs are acid, as at Lyncestus and in Italy in the Velian country, at Teano in Campania, and in many other places. These when used in drinks have the power of breaking up stones in the bladder, which form in the human body.

In setting out the walls of a city the choice of a healthy situation is of the first importance: it should be on high ground, neither subject to fogs nor rains; its aspects should be neither violently hot nor intensely cold, but temperate in both respects.