It must be remembered that although broad classifications can be made in styles, yet there are intermediate stages which are transitional, and which are usually due to the importation of some foreign influence. The phases of a transitional period can usually be defined; at first the new style is slavishly imitated or else executed by the foreign worker exploiting it. This is followed by its being used in conjunction with the native construction, and lastly, the native interpretation of the foreign style is possibly grafted on to older forms. It should be understood that at no time was there any great immediate change in style, but that there are phases which can be described as typical, connected by periods of gradual change or transition; due, doubtless, to individual expression of taste, either on the part of exponent or patron, or as previously suggested, by influences political, religious or commercial. Careful study will show that the change in the majority of instances was due to reaction from a florid to a more severe treatment, which in its turn became redundant in character and detail. Apart from the artistic point of view, these changes are interesting as reflective of the character of the times. From the constructive point of view there are two distinct principles to be appreciated, the Lintel and the Arch. The Lintel, which is the earlier, may be described as a large stone style, and consists of the bridging of apertures by means of horizontal slabs, supported by vertical columns or piers. This is a method of construction with distinct limitations, as it was impossible to bridge large areas or spaces without frequent support. _The Lintel_ [Illustration: No. 4. The Lintel.] The joints of the Lintel necessarily occur over the centres of the supporting columns, and the space between was controlled by the size of the obtainable material and the imposed weight it could bear; the result being, as in the great hall at Karnak, a forest of closely spaced columns. It was not until the principle of the Arch was developed into vaulting that interiors of any considerable dimension with clear floor spaces were possible. Lintel construction was employed in the Egyptian, Chaldean and Greek styles. 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. [Illustration: 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.