MASONRY STRUCTURES. – Having abandoned the natural shelters of caves and built rudimentary dwellings, man formed agglomerations which he enclosed with earthworks and ditches to defend both men and herds. In due course, to make the defence more effective, he employed rough-hewn stones, scattered, poorly bonded and disjointed. When, later, he learned the technique of cutting with siliceous and then metallic tools, there arose, even in the Neolithic age, the first megalithic enclosures of Mediterranean civilisation (Crete, Malta, Sardinia, the Balearics), consisting mostly of a base course of large stones or slabs, either corbelled or orthostatic, surmounted by courses of stones of diminishing size.
The progressive refinement of these defensive constructions on hilltops, around settlements and sacred sites, as building techniques and methods of extraction and dressing improved, led, during the Copper and Iron Ages, to the erection of those marvellous colossal monuments of prodigious solidity, made of large irregular polygonal stones fitted together without mortar, merely by overlapping. Such are the walls of Tiryns and many sites in Greece, Asia Minor and the Iberian Peninsula. Their grandeur is such that later ages could no longer comprehend the expenditure of effort required to build them and attributed their construction to the fabulous Cyclopes (cyclopean walls). The technique of transporting and stacking such massive stones, even with the aid of levers, rollers, partial embankments and inclined planes, is astonishing.
I. PELASGIC WALLS
A later, more refined phase of such constructions is that in which the stones are better worked and dressed so as to fit together more closely and are more carefully bonded (walls of Mycenae in the Argolid). A further phase is that in which the tendency towards regularity is more pronounced; the stones are laid in horizontal courses of fairly uniform size. Such are the walls of Argos, Messene (371 BC), Athens and the Piraeus. These constructions, dating from the 7th to the 4th centuries BC, are characteristic of the indigenous populations of Greece and Italy and were called Pelasgic because they were attributed to the first immigrants from Greece to Italy, known as Pelasgi. In reality, they belong to the indigenous populations of Greece and Italy of Mediterranean origin; in Italy, to the Italic peoples. Examples include the walls built at different times, from the most remote to historical periods, to defend the arces and settlements of the Italic peoples of central Italy (Cortona, Rieti, Alba Fucens, Tusculum, Praeneste, Cora, Signia, Norba, Cireglio, Terracina, Ferentinum, Alatri, Arpinum, Atina, etc.).II. OPUS QUADRATUM
While polygonal masonry was used in Italic towns whose nearby terrain was calcareous, in Etruria, Rome and Latium a more advanced and aesthetically pleasing type of wall construction was adopted, facilitated by the availability of tufa, a lighter and easily worked material. The stones, of varying size, were first roughly squared and laid in somewhat irregular courses (remains of walls on the Palatine, Aventine, Ardea and Veii), then gradually became more regular; such are the so-called Servian walls of Rome (4th century BC). These consist of large blocks of compact tufa (lithoid) from the quarries of Fidenae and Veii, laid in alternating courses of headers and stretchers, bearing marks of extraction from the quarries. Horizontal courses are interrupted by arches to give the walls greater solidity. Opus quadratum was used for the tholos cisterns of the Germalus, the primitive walls of the Regia in the Forum, the foundations of the temples of Jupiter Capitolinus, Saturn, the Dioscuri, Concordia, the *Rostra vetera* and the ogival cistern of Tusculum (5th–4th centuries BC). If the courses are of equal height, opus quadratum is termed *isodomum*; if unequal, *pseudo-isodomum*. The primitive temples have their facing in this tufa, peperino or other local stone, coated with stucco. Some other buildings of the Republican period, even late Republican, are in opus quadratum; the use of travertine (*lapis Tiburtinus*) became widespread, as, for example, in the Tabularium.III. OPUS INCERTUM
This is the type of Roman masonry consisting of a gradual reduction of polygonal work; it is also called opus antiquum. The core is formed by a rubble fill (emplecton, opus caementicium) faced with small limestone blocks as they came from the quarries, uncut, laid without order one upon another, bonded with mortar and completed with chips in the interstices (caementa). This technique is characteristic of the late 2nd and early 1st centuries BC and marks the remains of buildings erected and rebuilt during the renewal of Rome and the towns of Latium and central Italy after the destructions caused by the civil wars (88–82 BC), during the dictatorship of Sulla (82–78 BC); examples include the remains of the *Emporium* in Rome and the Sullan constructions at Palestrina, Terracina, etc.Opus incertum inaugurates the series of properly Roman masonry techniques whose robustness, proverbial for its strength, is due to the cohesive force of the materials employed: excellent-quality lime and pozzolana.
IV. OPUS RETICULATUM
In the first half of the 1st century BC there appears a type of masonry that is an improvement on opus incertum. The facing is formed of regularly squared wedges shaped like small truncated pyramids, with the base on the façade, arranged in diagonal lines inclined at 45° to the plane, so as to give the appearance of a net; the corners are reinforced with clamps of tufa blocks. In the first phase of this technique, up to the age of Julius Caesar, we have opus reticulatum, in which the lines are still uncertain and irregular and the layer of lime between the tesserae is still visible. Under Augustus the reticulation becomes more precise and this type of masonry predominates (House of Livia on the Palatine, remains of houses beneath the Flavian palace); under Nero it reaches perfection.OPUS LATERITIUM
During the feverish building activity of the Augustan age, the manufacture of bricks (*lateres*) made from potter’s clay, fired in a kiln, in square, rectangular, or triangular shapes, began to develop. These were used in masonry construction, initially for minor buildings and private houses. This type of masonry can in a certain way be considered a practical derivation of *opus quadratum*. Under Tiberius, the use of such facing became common and was for the first time widely employed in public buildings, such as the *Domus Tiberiana* on the Palatine and the *Castra Praetoria*. Its use became increasingly widespread for all types of buildings; in thermal structures, *opus latericium* was covered with a waterproof layer of *cocciopesto* (*opus signinum*).
Already before the Flavian period, but especially during the second half of the 2nd and early 3rd centuries of the Empire, decorative use became fashionable, featuring exposed brick curtains of carved and polychrome bricks, yellow, red, and brown in color (the sepulchral monument of Annia Regilla at the Caffarella, tombs along the Via Latina). Under Hadrian, brickwork triumphed fully and was made more solid by the adoption of courses of large bipedales bricks (59 x 59 cm) spaced about five feet apart (Pantheon, Mausoleum of Hadrian, Baths of Caracalla). For the centering of arches, *pedales* bricks (45 cm on a side) were used, and for the hypocausts of baths, *besas* bricks (22 cm on a side).
Each brick often bears a stamp indicating the clay quarry (*praedia*) and the brickworks (*figlina*, *officina*), along with the names of the owners and managers. The date of manufacture is frequently mentioned; innumerable are the *lateres reti* dated to the year 123 (consulship of Paetinus and Apronianus), evidence of the widespread use of brick material during the reign of Hadrian. In some cases, the intended use of the material is also indicated (e.g., *Castra Praetoria*, the Port of Claudius, and the Port of Trajan at Centumcellae).
The most common stamp shapes are crescent-shaped; square and semicircular stamps also occur, and after Diocletian, round and rectangular ones appear. The criterion for dating *opus latericium* is generally the thickness of the lime mortar layer between the brick courses: the thinner it is, the older the work. It must also be considered that the masonry may appear imperfect even if of good date, if it was intended to be covered with plaster. Many of the arches of the aqueducts supplying water to Rome were built in brick, with corner reinforcements in stone.
OPUS MIXTUM
Toward the end of the 1st century of the Empire, the practice began of combining the two systems—reticulated work and brickwork—in alternating layers. This type of masonry became common in the time of Trajan and Hadrian. Much of Hadrian’s Villa at Tivoli was built with walls composed of three rows of bricks alternating with broad layers of *opus reticulatum*, all reinforced at the corners with brick clamps. Toward the end of the 2nd century, under the Antonines, there was a characteristic carelessness in the execution of the reticulated work, giving the impression that in that period the *opus incertum* of the Republican age had come back into fashion. Such deteriorated reticulated work, reinforced with *caementa* of varying sizes, appears in masonry from the late 2nd, 3rd, and even 4th centuries, either alone or alternated with brick courses—another type of mixed masonry.
Toward the end of the 3rd and early 4th centuries, important brick constructions were still being carried out. A fairly tight curtain wall is found in the Aurelian Walls of Rome, begun by Aurelian in 275. Other imposing brick structures in Rome include the Baths of Diocletian, the Basilica of Maxentius, the *Sessorianum*, etc. In the Late Empire, a type of masonry that had been little used since the end of the 2nd century gained ascendancy: horizontal bands of fired bricks alternated with layers of squared blocks of tufa or stone (Villa of the Quintili, Circus of Maxentius on the Appian Way, ca. 310). Over time, this construction method became increasingly hasty and imperfect. The layer of mortar between the courses grew ever thicker; in some cases, as early as the beginning of the 4th century, it exceeded the thickness of the bricks themselves. An even more practical and economical system involved building walls with elongated chips of tufa or flint, laid in nearly horizontal courses with sharp edges and little mortar.
LE S. M. NELLE CHIESE DI ROMA
The Commission established within the Center for the Study of Architectural History has highlighted that in Rome, church construction in the 4th and 5th centuries was either in *opus latericium* or in striped masonry (*opus mixtum*). These techniques are found combined in the Mausoleum of Constantina (S. Costanza); they are in brickwork in the foundations of the apses of the Constantinian Basilicas of the Lateran and the Vatican, and in the basilicas of S. Maria Maggiore, S. Pietro in Vincoli, S. Sabina, S. Sisto Vecchio, S. Agata dei Goti, and S. Stefano Rotondo.
Striped masonry is found in the foundations of the Basilica of S. Pietro in Vaticano and in the basilicas of S. Sebastiano, of the martyrs Faustinus, Simplicius, and Beatrice on the Via Portuense, and of the title of Vestina (S. Vitale). For the 8th century, structures are attested in S. Angelo in Peschiera, ca. 755 (R. Krautheimer, op. cit. in bibliography, pp. 74–76), and in S. Eusebio from the time of Pope Zachary or Adrian I (772–95; ibid., p. 213, fig. 128).
For the 9th century, structures are found in the churches of S. Susanna, of SS. Nereo and Achilleo, and of S. Stefano Maggiore in the Vatican, from the time of Leo III (795–816) (R. Krautheimer – W. Frankl, *Recent discoveries in churches in Rome*, in *American Journal of Archaeology*, 43 [1939], pp. 388 ff. and fig. 56), of S. Cecilia (R. Krautheimer, see op. cit. in bibliography, pp. 106, 108, fig. 70), and of S. Prassede from the time of Paschal I (817–24). — See pl. CII.