We continue with the third part of this serie of four articles about the main Roman masonry techniques.
Oppus Testaceum. This constructive technique, invented by the Romans, is the one that uses the baked brick: much harder, more resistant and more durable than the traditional clay/mud brick, without firing, whose constructive technique was named Oppus Latericium. The size of the Roman baked bricks generally followed a module normalized in 3 different measurements -photo 1-- each of them with its own name: bipedal (two feet each long side, 59.2 cms), bessal (the most small, 2/3 of foot each long side, 19,7 cms) and sesquipedal (1,5 feet). This last one could be divided in triangles. In the case of clay/mud bricks, there were also three kinds of brick namely: lydian brick (with dimensions of 1 foot by half foot, 29.6 x 18.8 cm), tetradorum brick (four spans, 1 foot by 1 foot, 29.6 x 29.6 cm) and the pentadron brick (five spans or what is equal 37 x 37 cm). Although they were usually of rectangular geometry, examples of tubular (circular and square section) and circular bricks (semi-cylindrical, cylindrical and quarter-cylindrical), used respectively on roofs and columns - photo 2 -, are not lacking. There are also cases of bricks cut into capricious shapes intended to draw designs with which to adorn the facades of monuments. This particular constructive technique is denominated Oppus Figlinum.
Photo 1.- Set of Roman bricks with different module. Roman city of Regina. Casas de Reina, Badajoz, Spain. 2nd century AD.
Arranged in longitudinal rows joined with lime mortar -photo 3-, the fired brick, hereinafter referred to simply as brick, proved from the beginning (first century BC) to be an optimal material for construction due to its cheapness and good technical characteristics, to the point of rapidly becoming widespread throughout the Empire. In fact, many of the constructions of early imperial period were built with this material and not with stone. This preference for brick will reach its zenith in the last two centuries of the Empire, when the available money for the erection of new buildings was being reduced year after year together with the splendor and the power of Rome.
Photo 2.- Ancient city of Carteia. San Roque, Cádiz, Spain. Quarter-cylindrical bricks used in the construction of columns.
Regarding the modes of use, they were mainly two: as a main structural element, support of the weight and the tensions of the structure in question and as lost formwork to be filled later with the usual Oppus Caementicum more or less rough –rubble agglomerated with lime mortar in many cases--. In the first case, usual in non-critical structures such as small vaults, dividing walls, openings and others, the advantage of the brick lay mainly in its great cheapness and ease of use combined with its suitability to make demanding geometric shapes as, for example, the typical Roman arches. When, on the contrary, the burdens to be borne by the future structure were high enough to discourage the exclusive use of the Oppus Testaceum, the walls were raised in the very robust Oppus Caementicum: more expensive to execute but still economical. Having said this, it is easy to understand the second way of using brick: without a doubt the most used cladding throughout the imperial era, well ahead of the Oppus Spicatum and Reticulatum, which in fact were practically relegated by the Oppus Testace