The Arch, as a constructive form, did not appear until a later period, and possibly was due to some extent to the employment of brick and stones of small size.
No. 5. Tomb of Tantalus in Lydia. Vault form, but not vault construction.
Form or shape is not involved, as it is quite possible to so shape the Lintel as to give the appearance of the Arch by cutting the underside to the required curve. In the early Greek architecture examples have been found of both Arch and vault appearance, but these are the result of horizontal courses, successively projecting; that is, built in the form of inverted steps, the underside being cut to the arch curve, and is a form of construction restricted to bridging relatively small areas.
The Arch
No. 6. A. Structural Arch. B. Arch appearance, result of cutting away.
The principle of the Arch depends upon the separate pieces of material being formed to a wedge shape, the joints corresponding to radial lines drawn through the centre from which the Arch curve is struck.