Masonry Structures

MASONRY STRUCTURES. - When man abandoned the natural shelters of caves and built rudimentary dwellings, he formed settlements which he enclosed with earthworks and ditches for the defense of men and herds. In the course of time, to make the defense more effective, he used shapeless scattered blocks of stone, poorly fitted and disconnected. Once the technique of cutting was later mastered through the use of flint and then metal tools, the first megalithic enclosures of Mediterranean civilization arose, as early as the Neolithic age (Crete, Malta, Sardinia, the Balearic Islands), formed for the most part by a base course of large blocks or slabs, laid flat or set upright, with above it a course of several superimposed rows of blocks of decreasing proportions.

The progressive perfecting of these defensive constructions on the heights, around settlements and sacred places, with the advance of building technique and of the means of extracting and adapting the material, led, throughout the Eneolithic and Iron ages, to the erection of those marvelous colossal monuments, of prodigious solidity, made of large blocks of stone in irregular polygons, joined without cement by mere superimposition. Such are the walls of Tiryns and of many localities in Greece, Asia Minor and the Iberian Peninsula. Their grandeur is such that in a later age so imposing an expenditure of effort to build them could no longer be understood, and their erection was attributed to the fabulous giants the Cyclopes (Cyclopean walls). The technique of transporting and superimposing such great blocks is astonishing, even if it was achieved by the use of levers, rollers, partial embankments and inclined planes.

I. PELASGIAN WALLS

A subsequent, more perfected phase of such constructions is the one in which the blocks are better worked and flattened so as to make them fit together and be more carefully joined (walls of Mycenae in the Argolid). A further phase is the one in which the tendency toward regularity is more pronounced; the stones are arranged in horizontal courses and are not very dissimilar from one another. Such are the walls of Argos, of Messene (371 B.C.), of Athens, of Piraeus. These constructions, dating to the centuries between the 7th and the 4th B.C., are characteristic of the indigenous populations of Greece and Italy and were called Pelasgian because they were attributed to the first immigrants from Greece into Italy, called Πέλαγος. In reality they belong to the indigenous populations of Greece and Italy of Mediterranean origin; in Italy, to the Italic peoples. Such are the walls erected in different ages, from the most remote to historical times, for the defense of the arces and the settlements of the Italic peoples of central Italy (Cortona, Rieti, Alba Fucens, Tusculum, Palestrina, Cori, Segni, Norba, Circello, Terracina, Ferentino, Alatri, Arpino, Atina, etc.).

II. OPUS QUADRATUM

While polygonal work flourished in the Italic cities whose nearby terrain had a limestone base, already in Etruria, in Rome and in Latium a still more advanced and aesthetic kind of wall construction was adopted, favored by the presence of tufa, a lighter material and easily worked. The blocks, of more or less large dimensions, are of cappellaccio, at first roughly squared and arranged in rather irregular courses (remains of walls of the Palatine, of the Aventine, of Ardea and of Veii), and gradually become more regular; such are the so-called Servian walls of Rome (4th century B.C.). These are made of large blocks of more compact (lithoid) tufa, from the quarries of Fidenae and Veii, in alternating layers placed head-wise and length-wise, bearing quarry marks. The horizontal planes are interrupted by arches to give greater solidity to the walls. In opus quadratum are built the tholos cisterns of the Germalus, the primitive walls of the Regia in the Forum, the bases of the temples of Jupiter Capitolinus, of Saturn, of the Castors, of Concord, of the Rostra vetera and the ogival cistern of Tusculum (5th-4th centuries B.C.). If the courses are of equal size the opus quadratum is called isodomum, if unequal, pseudo-isodomum. The primitive temples have their facings in this work of tufa, of peperino or of other local stone covered with stucco. Some other buildings of the Republican period, even a late one, are also in opus quadratum; the use of travertine (lapis Tiburtinus) spreads, as, for example, in the Tabularium.

III. OPUS INCERTUM

This is the name for that kind of Roman masonry consisting in a gradual reduction of polygonal work; it is also called opus antiquum. The core is formed by a rubble filling (emplecion, opus concretum) faced with a facing of small blocks of limestone such as came from the quarries, not squared, arranged without order one upon another, bonded with mortars and completed with chips in the interstices (caementa). This s. m. is characteristic of the end of the 2nd and the beginnings of the 1st century B.C. and characterizes the remains of buildings erected and rebuilt in the renewal of Rome and of the cities of Latium and central Italy, after the destructions produced by the civil wars (88-82 B.C.), during the dictatorship of Sulla (82-78 B.C.); examples of it are, among others, the remains of the Emporium in Rome and the Sullan constructions of Palestrina, of Terracina, etc.

Opus incertum begins the series of properly Roman masonry, whose strength, which has become proverbial, is due to the force of cohesion of the materials employed, lime of excellent quality and pozzolana.

IV. OPUS RETICULATUM

In the first half of the 1st century B.C. there appears a type of wall structure that is a refinement of opus incertum. The facing is formed of wedges regularly squared into the shape of so many small truncated pyramids, with the base on the face, arranged in oblique lines inclined at 45° to the plane, so as to give the appearance of a net; the corners are reinforced by bond-stones in tufa blocks. In the first phase of this work, that is, down to the age of Julius Caesar, one has the opus quasi-reticulatum, in which the lines are still uncertain and irregular and the layer of lime between the tesserae is still visible. With the Augustan period the reticulatum becomes more exact and becomes the predominant type of masonry (house of Livia on the Palatine, remains of houses beneath the palace of the Flavians); under the reign of Nero it reaches perfection.

V. OPUS LATERITIUM

During the feverish building activity of the Augustan age, the manufacture of bricks (lateres) developed, made from figuline clay, fired in a kiln, of square, rectangular or triangular shape, used in the construction of masonry, at first in minor buildings and private houses. This masonry work can in a certain way be considered a practical derivative of opus quadratum. Under Tiberius the use of such a facing became common and was for the first time widely employed in constructions of a public character, such as the Domus Tiberiana on the Palatine and the Castra Praetoria. Its use became ever more common for every kind of building; in bath buildings the opus lateritium is covered with an impermeable layer of crushed potsherds (opus signinum). Already before the age of the Flavians, but even more throughout the second half of the 2nd and at the beginning of the 3rd century of the Empire, the decorative use of a facing of cut and polychrome bricks, yellow, red, and brown in colour, was in fashion (tomb of Annia Regilla at the Caffarella, tombs of the Via Latina). With Hadrian brickwork triumphs fully and is made more solid by the adoption of courses of large bipedales bricks (59 × 59 cm.) at about five feet from one another (Pantheon, Mausoleum of Hadrian, Baths of Caracalla). For the centrings of arches the sesquipedales were used (45 cm. per side) and for the hypocausts of baths the bessales (22 cm. per side). Each brick very often bears the stamp with the indication of the clay pit (praedia) and of the workshop (figina, officina) and the names of the respective owners and managers. The mention of the date of issue is common; countless are the lateres bearing the date of the year 123 ("Paetino et Aproniano coss."), an indication of the great diffusion of brick material during the reign of Hadrian. In some cases the destination of the material is also indicated (Castra Praetoria, port of Claudius and port of Trajan at Centumcellae). The most frequent form of the stamps is the crescent-shaped one; there are also the square and the semicircular, and, after Diocletian, the round and the rectangular. The criterion for dating opus lateritium is given in general by the thickness of the layer of lime between the rows of bricks; the thinner it is, the older the work. Account must moreover be taken of the fact that the masonry may prove imperfect even if of good age, should it have been intended to be covered with plaster. For the most part the arches of the aqueducts bringing the waters to Rome are built in brickwork, with corner reinforcements in stone.

VI. OPUS MIXTUM

At the end of the 1st century of the Empire there began the practice of combining the two systems, the reticulate and the brickwork, in alternating layers. This kind of s. m. became common in the times of Trajan and Hadrian. A large part of Hadrian's Tiburtine Villa is built with walls formed of three rows of bricks alternating with broad layers of opus reticulatum, the whole reinforced at the corners with brick bonding blocks. At the end of the 2nd century, under the Antonines, there occurred a characteristic carelessness in the execution of the reticulate, so that one has the impression that in that age the opus incertum of the Republic had come back into fashion. A reticulate thus deteriorated, reinforced by caementa of various sizes used as filling, is found in walls of the end of the 2nd, the 3rd and even the 4th century, either alone, or alternating with rows of bricks, another kind of mixed work.

At the end of the 3rd and in the early 4th century there were still important brick constructions. A fairly close curtain is presented by the city wall of Rome, begun by Aurelian (275). Other imposing brick constructions in Rome are the Baths of Diocletian, the Basilica of Maxentius, the Sessorianum, etc. In the late Empire there prevails a wallwork, already in scant use since the end of the 2nd century, of horizontal bands of fired bricks alternating with layers of squared blocks of tufa or stone (Villa of the Quintilii, Circus of Maxentius on the Appian Way, A.D. 310). This structure appears in the course of time increasingly hurried and imperfect. The layer of lime between the courses becomes ever higher; in some cases, already at the beginning of the 4th century, it is greater in thickness than the bricks themselves. An even more practical and economical system was achieved by building walls by means of elongated chips of tufa or of flint, in almost horizontal layers and with sharp edges, with little mortar.

Gioacchino Mancini

VII. MASONRY STRUCTURES IN THE CHURCHES OF ROME

The Commission that arose within the Centro studi di Storia dell'architettura has brought to light that in Rome the construction of churches in the 4th and 5th centuries is either in opus latericium or in banded work (opus mixtum). They are found paired in the Mausoleum of Constantina (St. Costanza); they are in brickwork in the foundations of the apses of the Constantinian Basilicas of the Lateran and the Vatican, in the basilicas of St. Mary Major, of St. Peter in Chains, of St. Sabina, of St. Sisto Vecchio, of St. Agatha of the Goths, of St. Stephen Rotondo.

The foundations of the basilica of St. Peter in the Vatican are in banded work, as are those in the basilicas of St. Sebastian, of the martyrs Faustinus, Simplicius, and Beatrice on the Via Portuense, of the titulus of Vestina (St. Vitalis). For the 8th century there are structures in S. Angelo in Pescheria ca. 755 (R. Krautheimer, op. cit. in bibl., pp. 74-76), in S. Eusebio from the time of Pope Zachary or of Adrian I (772-95; ibid., p. 213, fig. 128).

For the 9th century there are the structures of the churches of S. Susanna, of Sts. Nereus and Achilleus and of S. Stefano Maggiore in the Vatican, from the time of Leo III (795-816) (R. Krautheimer - W. Frank), Recent discoveries in churches in Rome, in American Journal of Archaeology, 43 [1939], p. 388 ff. and fig. 56), of S. Cecilia (R. Krautheimer, v. op. cit. in bibl., pp. 106, 108, fig. 70), and of S. Prassede from the era of Paschal I (817-24). - See plate CII.

Enrico Josi