Roman monumental architecture emerged about the 6th century bce as an Italic style, closely related to that of the Etruscans. The Temple of Jupiter Capitolinus in Rome, built about this time, resembled Etruscan buildings in central Italy—at Signia, Orvieto, Veii, and elsewhere—in its podium (base or platform on which it rests), its triple cella, its broad low Etruscan porch, and its characteristic terra-cotta adornment. The Capitolium Temple at Cosa, a Roman foundation located northeast of Rome, was similarly conceived in the 3rd century bce. The forms, sculptural and spatial, had evolved locally in a tradition of wood and terra-cotta, though even at this time there was a slight Greek influence.

From about 200 bce to about 50 ce, the rise of republican Rome and the increasing contacts with Greece resulted in a Greek influence strong enough to control the sculptural forms and even to modify the spatial effects. A temple at Gabii, perhaps of the 3rd century, and the Temple of Apollo at Pompeii, of about 120 bce, had approximately the Greek single-cella, peripheral (having a single row of columns surrounding the building) plan; the latter retained the Italic podium and open porch, and it had pronounced modifications of the Greek Ionic order. Buildings such as the temple under the present church of San Nicola in Carcere (c. 31 bce) and the Temple of Fortuna Virilis (c. 40 bce), both in Rome, show the height of Hellenistic influence. But the slightly later Augustan temples of Concord, Castor, and Pollux in the Roman Forum, and Mars Ultor in the Forum of Augustus in Rome had a native freedom of arrangement of space and highly elaborated moldings, particularly in the entablature, where new forms, mostly floral, were lavishly displayed in finely worked, full masses, while consoles (projecting ornamental brackets) became increasingly important.

During this period the more peculiarly Roman concepts developed chiefly in secular architecture. The Stabian Baths at Pompeii, built perhaps as early as 120 bce, were already composed of vaulted spaces, though quite compactly and with little of the later freedom and spaciousness. In some buildings—such as the Carcer and Tullianum (prisonlike structures of about 100 bce or earlier) and the Tabularium of about 78 bce, all just west of the Forum in Rome—arches and concrete were basic, though orders influenced by Hellenistic architecture were used for ornament. The Theatre of Marcellus (c. 11–10 bce) was built with a high exterior facade where orders and arches blended—a type of theatrical design that became standard.

The beginning of Roman influence outside Italy is evident in theatres and amphitheatres at Arles and Nîmes (perhaps as early as 30 bce), in a temple built about 12 bce at Nîmes called the Maison-Carrée, and in small buildings in Greece and Syria built shortly thereafter.

About the middle of the 1st century ce there was a surge of development of spatial composition. The orders and other ornament inherited from Greece were increasingly modified and elaborated in nonfunctional perspective effects, and other kinds of ornament and spatial configurations gained importance. Buildings such as the Colosseum (80 ce) in Rome preserved a more conservative character, but with the baths and palaces of Nero began the series of imperial compositions of grand, elaborate spaces. The movement came to a climax under Trajan and Hadrian (c. 98–138), with Trajan’s Forum at Rome, the great complex of buildings at Baalbek in Syria, the Pantheon in Rome, and Hadrian’s Villa at Tivoli.

Through the 2nd and 3rd centuries countless buildings were erected in cities and towns throughout the empire, in part under imperial patronage and in part by local enterprise. Provincial buildings had great individuality, but the more ambitious usually followed the influence of the capital. Forms evolved by about 140 ce were followed conventionally for the next 50 years (and longer), but from about 200 ce to the age of Constantine there was a growing trend toward increased majesty and less emphasis on the material substance or appearance of a building. Even before the end of the 2nd century, deep cutting with sharply contrasting light and shadow had begun to detract from the impression of the solid forms in carved ornament. In the arches of Septimius Severus (c. 200 ce), for instance, light and shadow—not the masses of the forms of the motifs—formed the design. Especially in Africa, illogical composition of the elements of entablatures robbed them of structural significance. In the Palace of Diocletian (c. 300 ce), extensive use of arched colonnades emphasized movement rather than mass. The sheer faces of some wall surfaces, like those of towers flanking the gates, became austere geometric forms. Experimentation and elaboration in vaulting, as in the so-called Temple of Minerva Medica (c. 260 ce) at Rome, was directed toward making the supports lighter structurally and aesthetically. Compared with the Baths of Caracalla (c. 217 ce), the Basilica of Maxentius (c. 310–320 ce) was simpler in design and more concentrated, increasing its sense of elemental vastness and permanence, whereas in contrast to the Pantheon its shape and ornament are less tangible.

Finally, evolving into the early Christian art to come, the Constantinian mausoleum of Santa Costanza, with its dome resting on a drum supported on arches on a circle of pairs of slender columns, already was striving to suggest the independence of roof and space from material support.