The first step in the transformation of the architect’s grand design into the physical structure was in identifying and securing the supply of materials. The bulk of these materials are meant to comprise the basic structure; the lime and pozzolana of the mortar, the brick of the wall facing, and the basalt, tufa and pumice forming the core of the foundations, walls and vaults. A second large group of materials are those required during the process of construction but which do not form a permanent part of the finished structure, i.e. the timber and cords for scaffolding, formwork, lifting devices, and baskets for transport. Materials for decoration form a third major group, of which marble is by far the most important. The only other significant class of materials is metal, whether used in the structure, in the decoration, or in the plumbing.
It should never be under-estimated just how critical a factor it is to identify and secure a dependable supply of building materials to maintain an efficient and sucessful building project. This becomes even more important where the site is large and construction time short; laying the first stone assumes that stone, mortar and trowel are all at hand; finishing in time means that there are no interruptions to critical supplies. The essential considerations affecting a builder’s choice of basic materials include the location of source, the reliability, sufficiency, and quality of the material supplied, the ease of procurement, and the methods and routes of transport to the building site. All these factors are relevant to the Baths of Caracalla.
