Brick and concrete in Thursday’s Big and Tall class, and in brushing up on my Vitruvius this passage comes up:
17. The laws of the state forbid that walls abutting on public property should be more than a foot and a half thick. The other walls are built of the same thickness in order to save space. Now brick walls, unless two or three bricks thick, cannot support more than one story; certainly not if they are only a foot and a half in thickness. But with the present importance of the city and the unlimited numbers of its population, it is necessary to increase the number of dwelling-places indefinitely. Consequently, as the ground floors could not admit of so great a number living in the city, the nature of the case has made it necessary to find relief by making the buildings high. In these tall piles reared with piers of stone, walls of burnt brick, and partitions of rubble work, and provided with floor after floor, the upper stories can be partitioned off into rooms to very great advantage. The accommodations within the city walls being thus multiplied as a result of the many floors high in the air, the Roman people easily find excellent places in which to live.
18. It has now been explained how limitations of building space necessarily forbid the employment of brick walls within the city.
The translation here seems kind of weird, but the comment at the start of paragraph 18 makes it clear that Vitruvius’ objection is to walls of unfired brick, which was only half as strong as fired brick. If that’s the case, the point here is that unfired brick requires piers that are too large to meet the city’s building code.
Here’s the same argument, nearly 2000 years later, for why brick isn’t a suitable material for a tall urban building:
“The carrying strength of street walls for masonry construction is the carrying strength of the piers; that is, that part of these walls measured between the windows, and this fact limits the height of masonry buildings. The horizontal area of the piers either takes floor space or window area, and both alternatives are objectionable…. The lower floor piers are seven feet thick, in spite of using vitirified brick and cement mortar in their construction, figured to carry eighteen tons per square foot, dead and live load. The windows of these buildings might be better if they were wider, and the floor space taken in the lower floors by the walls is very valuable.”
Corydon T. Purdy, “The Evolution of High Building Construction.” Journal of the Western Society of Engineers, XXXVII, no. 4. August, 1932. 204-205. Note the “in spite of using vitrified brick,” then the strongest available.