Since such very powerful kings have not disdained walls built of brick, although... they might often have had them not only of masonry or dimension s… - Vitruvius

In walls of masonry the first question must be with regard to the sand, in order that it may be fit to mix into mortar and have no dirt in it. The kinds of pitsand are these: black, gray, red, and carbuncular. Of these the best will be found to be that which crackles when rubbed in the hand, while that which has much dirt in it will not be sharp enough. Again: throw some sand upon a white garment and then shake it out; if the garment is not soiled and no dirt adheres to it, the sand is suitable.

Lay a second foundation enough inside the first... Having laid these two foundations... build cross walls between them uniting the outer and inner foundation in a comb like arrangement set like teeth of a saw. With this form of construction the burden of earth will be distributed into small bodies and will not lie with all its weight in one crushing mass so as to thrust out substructures.

To guard against this, we must proceed as follows. Let down a lighted lamp, and if it keeps burning, a man may make the descent without danger.