Note Note 3 — Chapter I

(3) In the Delta, at least, the sizes of bricks from the Twenty-first Dynasty down to Arab times decrease very regularly; under the Twenty-first Dynasty they are about 18 x 9 x 5 inches; early in the Twenty-sixth, 16-1/2 x 8-1/4 x 5; later 15 x 7- 1/2; in early Ptolemaic times, 14 x 7; in Roman times, 12 x 6, in Byzantine times, 10 x 5; and Arab bricks are 8 x 4, and continue so very generally to our times. The thickness is always least certain, as it depends on the amount placed in the mould, but the length and breadth may in most cases be accepted as a very useful chronological scale.