A Text-Book of the History of Architecture Part 8

[Ill.u.s.tration: FIG. 55.--INTERIOR OF THE PANTHEON.]

[Ill.u.s.tration: FIG. 56.--EXTERIOR OF THE PANTHEON.

(From model in Metropolitan Museum, New York.)]

The exterior (Fig. 56) was less successful than the interior. The gabled porch of twelve superb granite columns 50 feet high, three-aisled in plan after the Etruscan mode, and covered originally by a ceiling of bronze, was a rebuilding with the materials and on the plan of the original p.r.o.naos of the Pantheon of Agrippa. The circular wall behind it is faced with fine brickwork, and displays, like the dome, many curious arrangements of discharging arches, reminiscences of traditional constructive precautions here wholly useless and fict.i.tious because only skin-deep. A revetment of marble below and plaster above once concealed this brick facing. The portico, in spite of its too steep gable (once filled with a "gigantomachia" in gilt bronze) and its somewhat awkward a.s.sociation with a round building, is nevertheless a n.o.ble work, its capitals in Pentelic marble ranking among the finest known examples of the Roman Corinthian. Taken as a whole, the Pantheon is one of the great masterpieces of the world's architecture.

[Ill.u.s.tration: FIG. 57.--FORUM AND BASILICA OF TRAJAN.]

+FORA AND BASILICAS.+ The fora were the places for general public a.s.semblage. The chief of those in Rome, the +Forum Magnum+, or +Forum Romanum+, was at first merely an irregular vacant s.p.a.ce, about and in which, as the focus of the civic life, temples, halls, colonnades, and statues gradually acc.u.mulated. These chance aggregations the systematic Roman mind reduced in time to orderly and monumental form; successive emperors extended them and added new fora at enormous cost and with great splendor of architecture. Those of Julius, Augustus, Vespasian, and Nerva (or Domitian), adjoining the Roman Forum, were magnificent enclosures surrounded by high walls and single or double colonnades.

Each contained a temple or basilica, besides gateways, memorial columns or arches, and countless statues. The +Forum of Trajan+ surpa.s.sed all the rest; it covered an area of thirty-five thousand square yards, and included, besides the main area, entered through a triumphal arch, the Basilica Ulpia, the temple of Trajan, and his colossal Doric column of Victory. Both in size and beauty it ranked as the chief architectural glory of the city (Fig. 57). The six fora together contained thirteen temples, three basilicas, eight triumphal arches, a mile of porticos, and a number of other public edifices.[14] Besides these, a net-work of colonnades covered large tracts of the city, affording sheltered communication in every direction, and here and there expanding into squares or gardens surrounded by peristyles.

[Footnote 14: Lanciani: _Ancient Rome in the Light of Recent Discoveries_, p. 89.]

[Ill.u.s.tration: FIG. 58.--BASILICA OF CONSTANTINE. PLAN.]

The public business of Rome, both judicial and commercial, was largely transacted in the _basilicas_, large buildings consisting usually of a wide and lofty central nave flanked by lower side-aisles, and terminating at one or both ends in an apse or semicircular recess called the _tribune_, in which were the seats for the magistrates. The side-aisles were separated from the nave by columns supporting a clearstory wall, pierced by windows above the roofs of the side-aisles.

In some cases the latter were two stories high, with galleries; in others the central s.p.a.ce was open to the sky, as at Pompeii, suggesting the derivation of the basilica from the open square surrounded by colonnades, or from the forum itself, with which we find it usually a.s.sociated. The most important basilicas in Rome were the +Semp.r.o.nian+, the +aemilian+ (about 54 B.C.), the +Julian+ in the Forum Magnum (51 B.C.), and the +Ulpian+ in the Forum of Trajan (113 A.D.). The last two were probably open basilicas, only the side-aisles being roofed. The Ulpian (Fig. 57) was the most magnificent of all, and in conjunction with the Forum of Trajan formed one of the most imposing of those monumental aggregations of columnar architecture which contributed so largely to the splendor of the Roman capital.

These monuments frequently suffered from the burning of their wooden roofs. It was Constantine who completed the first vaulted and fireproof basilica, begun by his predecessor and rival, Maxentius, on the site of the former Temple of Peace (Figs. 58, 59). Its design reproduced on a grand scale the plan of the tepidarium-halls of the thermae, the side-recesses of which were converted into a continuous side-aisle by piercing arches through the b.u.t.tress-walls that separated them. Above the imposing vaults of these recesses and under the cross-vaults of the nave were windows admitting abundant light. A _narthex_, or porch, preceded the hall at one end; there were also a side entrance from the Via Sacra, and an apse or tribune for the magistrates opposite each of these entrances. The dimensions of the main hall (325 85 feet), the height of its vault (117 feet), and the splendor of its columns and incrustations excited universal admiration, and exercised a powerful influence on later architecture.

[Ill.u.s.tration: FIG. 59.--BASILICA OF CONSTANTINE. RUINS.]

[Ill.u.s.tration: FIG. 60.--THERMae OF CARACALLA.

PLAN OF CENTRAL BLOCK.

A, _Caldarium, or Hot Bath_; B, _Intermediate Chamber_; C, _Tepidarium, or Warm Bath_; D, _Frigidarium, or Cold Bath_; E, _Peristyles_; a, _Gymnastic Rooms_; b, _Dressing Rooms_; c, _Cooling Rooms_; d, _Small Courts_; e, _Entrances_; v, _Vestibules_.]

+THERMae.+ The leisure of the Roman people was largely spent in the great baths, or _thermae_, which took the place substantially of the modern club. The establishments erected by the emperors for this purpose were vast and complex congeries of large and small halls, courts, and chambers, combined with a masterly comprehension of artistic propriety and effect in the sequence of oblong, square, oval, and circular apartments, and in the relation of the greater to the lesser ma.s.ses.

They were a combination of the Greek _palaestra_ with the Roman _balnea_, and united in one harmonious design great public swimming-baths, private baths for individuals and families, places for gymnastic exercises and games, courts, peristyles, gardens, halls for literary entertainments, lounging-rooms, and all the complex accommodation required for the service of the whole establishment. They were built with apparent disregard of cost, and adorned with splendid extravagance. The earliest were the +Baths of Agrippa+ (27 B.C.) behind the Pantheon; next may be mentioned those of +t.i.tus+, built on the substructions of Nero's Golden House. The remains of the +Thermae of Caracalla+ (211 A.D.) form the most extensive ma.s.s of ruins in Rome, and clearly display the admirable planning of this and similar establishments. A gigantic block of buildings containing the three great halls for cold, warm, and hot baths, stood in the centre of a vast enclosure surrounded by private baths, _exedrae_, and halls for lecture-audiences and other gatherings.

The enclosure was adorned with statues, flower-gardens, and places for out-door games. The +Baths of Diocletian+ (302 A.D.) embodied this arrangement on a still more extensive scale; they could accommodate 3,500 bathers at once, and their ruins cover a broad territory near the railway terminus of the modern city. The church of S. Maria degli Angeli was formed by Michael Angelo out of the _tepidarium_ of these baths--a colossal hall 340 87 feet, and 90 feet high. The original vaulting and columns are still intact, and the whole interior most imposing, in spite of later stucco disfigurements. The circular _laconic.u.m_ (sweat-room) serves as the porch to the present church. It was in the building of these great halls that Roman architecture reached its most original and characteristic expression. Wholly unrelated to any foreign model, they represent distinctively Roman ideals, both as to plan and construction.

[Ill.u.s.tration: FIG. 61.--ROMAN THEATRE. (HERCULANUM.) (From model.)]

[Ill.u.s.tration: FIG. 62.--COLOSSEUM. HALF PLAN.]

+PLACES OF AMUs.e.m.e.nT.+ The earliest Roman theatres differed from the Greek in having a nearly semicircular plan, and in being built up from the level ground, not excavated in a hillside (Fig. 61). The first theatre was of wood, built by Mummius 145 B.C., and it was not until ninety years later that stone was first subst.i.tuted for the more perishable material, in the theatre of Pompey. The +Theatre of Marcellus+ (23-13 B.C.) is in part still extant, and later theatres in Pompeii, Orange (France), and in the Asiatic provinces are in excellent preservation. The orchestra was not, as in the Greek theatre, reserved for the choral dance, but was given up to spectators of rank; the stage was adorned with a permanent architectural background of columns and arches, and sometimes roofed with wood, and an arcade or colonnade surrounded the upper tier of seats. The amphitheatre was a still more distinctively Roman edifice. It was elliptical in plan, surrounding an elliptical arena, and built up with continuous encircling tiers of seats. The earliest stone amphitheatre was erected by Statilius Taurus in the time of Augustus. It was practically identical in design with the later and much larger Flavian amphitheatre, commonly known as the +Colosseum+, begun by Vespasian and completed 82 A.D. (Fig. 62). This immense structure measured 607 506 feet in plan and was 180 feet high; it could accommodate eighty-seven thousand spectators. Engaged columns of the Tuscan, Ionic, and Corinthian orders decorated three stories of the exterior; the fourth was a nearly unbroken wall with slender Corinthian pilasters. Solidly constructed of travertine, concrete, and tufa, the Colosseum, with its imposing but monotonous exterior, almost sublime by its scale and seemingly endless repet.i.tion, but lacking in refinement or originality of detail and dedicated to b.l.o.o.d.y and cruel sports, was a characteristic product of the Roman character and civilization. At Verona, Pola, Capua, and many cities in the foreign provinces there are well-preserved remains of similar structures.

Closely related to the amphitheatre were the circus and the stadium. The +Circus Maximus+ between the Palatine and Aventine hills was the oldest of those in Rome. That erected by Caligula and Nero on the site afterward partly occupied by St. Peter's, was more splendid, and is said to have been capable of accommodating over three hundred thousand spectators after its enlargement in the fourth century. The long, narrow race-course was divided into two nearly equal parts by a low parapet, the _spina_, on which were the goals (_metae_) and many small decorative structures and columns. One end of the circus, as of the stadium also, was semicircular; the other was segmental in the circus, square in the stadium; a colonnade or arcade ran along the top of the building, and the entrances and exits were adorned with monumental arches.

+TRIUMPHAL ARCHES AND COLUMNS.+ Rome and the provincial cities abounded in monuments commemorative of victory, usually single or triple arches with engaged columns and rich sculptural adornments, or single colossal columns supporting statues. The arches were characteristic products of Roman design, and some of them deserve high praise for the excellence of their proportions and the elegance of their details. There were in Rome in the second century A.D., thirty-eight of these monuments. The +Arch of t.i.tus+ (71-82 A.D.) is the simplest and most perfect of those still extant in Rome; the arch of +Septimius Severus+ in the Forum (203 A.D.) and that of +Constantine+ (330 A.D.) near the Colosseum, are more sumptuous but less pure in detail. The last-named was in part enriched with sculptures taken from the earlier arch of Trajan. The statues of Dacian captives on the attic (_attic_ = a species of subordinate story added above the main cornice) of this arch were a fortunate addition, furnishing a _raison-d'etre_ for the columns and broken entablatures on which they rest. Memorial columns of colossal size were erected by several emperors, both in Rome and abroad. Those of +Trajan+ and of +Marcus Aurelius+ are still standing in Rome in perfect preservation.

The first was 140 feet high including the pedestal and the statue which surmounted it; its capital marked the height of the ridge levelled by the emperor for the forum on which the column stands. Its most striking peculiarity is the spiral band of reliefs winding around the shaft from bottom to top and representing the Dacian campaigns of Trajan. The other column is of similar design and dimensions, but greatly inferior to the first in execution. Both are really towers, with interior stair-cases leading to the top.

[Ill.u.s.tration: FIG. 63.--ARCH OF CONSTANTINE.

(From model in Metropolitan Museum, New York.)]

+TOMBS.+ The Romans developed no special and national type of tomb, and few of their sepulchral monuments were of large dimensions. The most important in Rome were the pyramid of +Caius Cestius+ (late first century B.C.), and the circular tombs of +Cecilia Metella+ (60 B.C.), +Augustus+ (14 A.D.) and +Hadrian+, now the Castle of S. Angelo (138 A.D.). The latter was composed of a huge cone of marble supported on a cylindrical structure 230 feet in diameter standing on a square podium 300 feet long and wide. The cone probably once terminated in the gilt bronze pine-cone now in the Giardino della Pigna of the Vatican. In the Mausoleum of Augustus a mound of earth planted with trees crowned a similar circular base of marble on a podium 220 feet square, now buried.

The smaller tombs varied greatly in size and form. Some were vaulted chambers, with graceful internal painted decorations of figures and vine patterns combined with low-relief enrichments in stucco. Others were designed in the form of altars or sarcophagi, as at Pompeii; while others again resembled aediculae, little temples, shrines, or small towers in several stories of arches and columns, as at St. Remy (France).

+PALACES AND DWELLINGS.+ Into their dwellings the Romans carried all their love of ostentation and personal luxury. They antic.i.p.ated in many details the comforts of modern civilization in their furniture, their plumbing and heating, and their utensils. Their houses may be divided into four cla.s.ses: the palace, the villa, the _domus_ or ordinary house, and the _insula_ or many-storied tenement built in compact blocks. The first three alone concern us, and will be taken up in the above order.

The imperial +palaces+ on the Palatine Hill comprised a wide range in style and variety of buildings, beginning with the first simple house of Augustus (26 B.C.), burnt and rebuilt 3 A.D. Tiberius, Caligula, and Nero added to the Augustan group; Domitian rebuilt a second time and enlarged the palace of Augustus, and Septimius Severus remodelled the whole group, adding to it his own extraordinary seven-storied palace, the Septizonium. The ruins of these successive buildings have been carefully excavated, and reveal a remarkable combination of dwelling-rooms, courts, temples, libraries, basilicas, baths, gardens, peristyles, fountains, terraces, and covered pa.s.sages. These were adorned with a profusion of precious marbles, mosaics, columns, and statues. Parts of the demolished palace of Nero were incorporated in the substructions of the Baths of t.i.tus. The beautiful arabesques and plaster reliefs which adorned them were the inspiration of much of the fresco and stucco decoration of the Italian Renaissance. At Spalato, in Dalmatia, are the extensive ruins of the great +Palace of Diocletian+, which was laid out on the plan of a Roman camp, with two intersecting avenues (Fig. 64). It comprised a temple, mausoleum, basilica, and other structures besides those portions devoted to the purposes of a royal residence.

[Ill.u.s.tration: FIG. 64.--PALACE OF DIOCLETIAN. SPALATO.]

The +villa+ was in reality a country palace, arranged with special reference to the prevailing winds, exposure to the sun and shade, and the enjoyment of a wide prospect. Baths, temples, _exedrae_, theatres, tennis-courts, sun-rooms, and shaded porticoes were connected with the house proper, which was built around two or three interior courts or peristyles. Statues, fountains, and colossal vases of marble adorned the grounds, which were laid out in terraces and treated with all the fantastic arts of the Roman landscape-gardener. The most elaborate and extensive villa was that of +Hadrian+, at Tibur (Tivoli); its ruins, covering hundreds of acres, form one of the most interesting spots to visit in the neighborhood of Rome.

[Ill.u.s.tration: FIG. 65.--HOUSE OF PANSA, POMPEII.

s, _Shops_; v, _Vestibule_; f, _Family Rooms_; k, _Kitchen_; l, _Lavarium_; _P, P, P_, _Peristyles_.]

There are few remains in Rome of the +domus+ or private house. Two, however, have left remarkably interesting ruins--the +Atrium Vestae+, or House of the Vestal Virgins, east of the Forum, a well-planned and extensive house surrounding a cloister or court; and the +House of Livia+, so-called, on the Palatine Hill, the walls and decorations of which are excellently preserved. The typical Roman house in a provincial town is best ill.u.s.trated by the ruins of Pompeii and Herculanum, which, buried by an eruption of Vesuvius in 79 A.D., have been partially excavated since 1721. The Pompeiian house (Fig. 65) consisted of several courts or _atria_, some of which were surrounded by colonnades and called _peristyles_. The front portion was reserved for shops, or presented to the street a wall unbroken save by the entrance; all the rooms and chambers opened upon the interior courts, from which alone they borrowed their light. In the brilliant climate of southern Italy windows were little needed, as sufficient light was admitted by the door, closed only by portieres for the most part; especially as the family life was pa.s.sed mainly in the shaded courts, to which fountains, parterres of shrubbery, statues, and other adornments lent their inviting charm. The general plan of these houses seems to have been of Greek origin, as well as the system of decoration used on the walls.

These, when not wainscoted with marble, were covered with fantastic, but often artistic, painted decorations, in which an imaginary architecture as of metal, a fantastic and arbitrary perspective, illusory pictures, and highly finished figures were the chief elements. These were executed in brilliant colors with excellent effect. The houses were lightly built, with wooden ceilings and roofs instead of vaulting, and usually with but one story on account of the danger from earthquakes. That the workmanship and decoration were in the capital often superior to what was to be found in a provincial town like Pompeii, is evidenced by beautiful wall-paintings and reliefs discovered in Rome in 1879 and now preserved in the Museo delle Terme. More or less fragmentary remains of Roman houses have been found in almost every corner of the Roman empire, but nowhere exhibiting as completely as in Pompeii the typical Roman arrangement.

+WORKS OF UTILITY.+ A word should be said about Roman engineering works, which in many cases were designed with an artistic sense of proportion and form which raises them into the domain of genuine art. Such were especially the bridges, in which a remarkable effect of monumental grandeur was often produced by the form and proportions of the arches and piers, and an appropriate use of rough and dressed masonry, as in the Pons aelius (Ponte S. Angelo), the great bridge at Alcantara (Spain), and the Pont du Gard, in southern France. The aqueducts are impressive rather by their length, scale, and simplicity, than by any special refinements of design, except where their arches are treated with some architectural decoration to form gates, as in the Porta Maggiore, at Rome.

+MONUMENTS:+ (Those which have no important extant remains are given in italics.) TEMPLES: _Jupiter Capitolinus_, 600 B.C.; _Ceres, Liber, and Libera_, 494 B.C. (ruins of later rebuilding in S. Maria in Cosmedin); _first T. of Concord_ (rebuilt in Augustan age), 254 B.C.; _first marble temple_ in _portico of Metellus_, by a Greek, Hermodorus, 143 B.C.; temples of Fortune at Praeneste and at Rome, and of "Vesta" at Rome, 83-78 B.C.; of "Vesta" at Tivoli, and of Hercules at Cori, 72 B.C.; _first Pantheon_, 27 B.C. In Augustan Age temples of _Apollo_, Concord rebuilt, Dioscuri, _Julius_, _Jupiter Stator_, _Jupiter Tonans_, Mars Ultor, Minerva (_at Rome_ and a.s.sisi), Maison Carree at Nimes, Saturn; at Puteoli, Pola, etc. _T. of Peace_; _T. Jupiter Capitolinus_, rebuilt 70 A.D.; temple at Brescia. Temple of Vespasian, 96 A.D.; also _of Minerva_ in Forum of Nerva; _of Trajan_, 117 A.D.; second Pantheon; T. of Venus and Rome at Rome, and of Jupiter Olympius at Athens, 135-138 A.D.; Faustina, 141 A.D.; many in Syria; temples of Sun at _Rome_, Baalbec, and Palmyra, cir. 273 A.D.; of Romulus, 305 A.D. (porch S. Cosmo and Damiano). PLACES OF a.s.sEMBLY: FORA--Roman, Julian, 46 B.C.; Augustan, 40-42 B.C.; _of Peace_, 75 A.D.; Nerva, 97 A.D.; Trajan (by Apollodorus of Damascus, 117 A.D.) BASILICAS: _Semp.r.o.nian_, _aemilian_, 1st century B.C.; Julian, 51 B.C.; _Septa Julia_, 26 B.C.; the Curia, later rebuilt by Diocletian, 300 A.D. (now Church of S. Adriano); _at Fano_, 20 A.D. (?); Forum and Basilica at Pompeii, 60 A.D.; of Trajan; of Constantine, 310-324 A.D. THEATRES (th.) and AMPHITHEATRES (amp.): th. _Pompey_, 55 B.C.; of _Balbus_ and of Marcellus, 13 B.C.; th.

and amp. at Pompeii and Herculanum; Colosseum at Rome, 78-82 A.D.; th. at Orange and in Asia Minor; amp. at Albano, Constantine, Nimes, Petra, Pola, Reggio, Trevi, Tusculum, Verona, etc.; amp.

Castrense at Rome, 96 A.D. Circuses and stadia at Rome. THERMae: of Agrippa, 27 B.C.; _of Nero_; of t.i.tus, 78 A.D. _Domitian_, 90 A.D.; Caracalla, 211 A.D.; Diocletian, 305 A.D.; _Constantine_, 320 A.D.; "Minerva Medica," 3d or 4th century A.D. ARCHES: _of Stertinius_, 196 B.C.; _Scipio_, 190 B.C.; _Augustus_, 30 B.C.; t.i.tus, 71-82 A.D.; _Trajan_, 117 A.D.; Severus, 203 A.D.; Constantine, 320 A.D.; of Drusus, Dolabella, Silversmiths, 204 A.D.; Ja.n.u.s Quadrifrons, 320 A.D. (?); all at Rome. Others at Benevento, Ancona, Rimini in Italy; also at Athens, and at Reims and St. Chamas in France. Columns of Trajan, _Antoninus_, Marcus Aurelius at Rome, others at Constantinople, Alexandria, etc.

TOMBS: along Via Appia and Via Latina, at Rome; Via Sacra at Pompeii; tower-tombs at St. Remy in France; rock-cut at Petra; at Rome, of Caius Cestius and Cecilia Metella, 1st century B.C.; of Augustus, 14 A.D.; Hadrian, 138 A.D. PALACES and PRIVATE HOUSES: On Palatine, of Augustus, Tiberius, Nero, Domitian, Septimius Severus, _Elagabalus_; Villa of Hadrian at Tivoli; palaces of Diocletian at Spalato and _of Constantine_ at Constantinople.

House of Livia on Palatine (Augustan period); of Vestals, rebuilt by Hadrian, cir. 120 A.D. Houses at Pompeii and Herculanum, cir.

60-79 A.D.; Villas of Gordia.n.u.s ("Tor' de' Schiavi," 240 A.D.), and _of Sall.u.s.t_ at Rome and _of Pliny_ at Laurentium.

CHAPTER X.

EARLY CHRISTIAN ARCHITECTURE.

BOOKS RECOMMENDED: Bunsen, _Die Basiliken christlichen Roms_.

Butler, _Architecture and other Arts in Northern Central Syria_.

Corroyer, _L'architecture romane_. c.u.mmings, _A History of Architecture in Italy_. Essenwein (Handbuch d. Architektur), _Ausgange der kla.s.sischen Baukunst_. Gutensohn u. Knapp, _Denkmaler der christlichen Religion_. Hubsch, _Monuments de l'architecture chretienne_. Lanciani, _Pagan and Christian Rome_.

Mothes, _Die Basilikenform bei den Christen_, etc. Okely, _Development of Christian Architecture in Italy_. Von Quast, _Die altchristlichen Bauwerke zu Ravenna_. De Rossi, _Roma Sotterranea_. De Vogue, _Syrie Centrale_; _eglises de la Terre Sainte_.

+INTRODUCTORY.+ The official recognition of Christianity in the year 328 by Constantine simply legalized an inst.i.tution which had been for three centuries gathering momentum for its final conquest of the antique world. The new religion rapidly enlisted in its service for a common purpose and under a common impulse races as wide apart in blood and culture as those which had built up the art of imperial Rome. It was Christianity which reduced to civilization in the West the Germanic hordes that had overthrown Rome, bringing their fresh and hitherto untamed vigor to the task of recreating architecture out of the decaying fragments of cla.s.sic art. So in the East its life-giving influence awoke the slumbering Greek art-instinct to new triumphs in the arts of building, less refined and perfect indeed, but not less sublime than those of the Periclean age. Long before the Constantinian edict, the Christians in the Eastern provinces had enjoyed substantial freedom of worship. Meeting often in the private basilicas of wealthy converts, and finding these, and still more the great public basilicas, suited to the requirements of their worship, they early began to build in imitation of these edifices. There are many remains of these early churches in northern Africa and central Syria.

+EARLY CHRISTIAN ART IN ROME.+ This was at first wholly sepulchral, developing in the catacombs the symbols of the new faith. Once liberated, however, Christianity appropriated bodily for its public rites the basilica-type and the general substance of Roman architecture.

Shafts and capitals, architraves and rich linings of veined marble, even the pagan Bacchic symbolism of the vine, it adapted to new uses in its own service. Constantine led the way in architecture, endowing Bethlehem and Jerusalem with splendid churches, and his new capital on the Bosphorus with the first of the three historic basilicas dedicated to the Holy Wisdom (Hagia Sophia). One of the greatest of innovators, he seems to have had a special predilection for circular buildings, and the tombs and baptisteries which he erected in this form, especially that for his sister Constantia in Rome (known as Santa Costanza, Fig. 66), furnished the prototype for numberless Italian baptisteries in later ages.