WHATEVER THE GENEALOGY OF ROME'S GREATNESS, IT IS NOT PREMISED on geography. The city's physical advantages are undeniably significant, but hardly peremptory; when all is said and done, the natural setting seems a poor match for such a glorious destiny. Ancient Rome had no natural seaport and never dominated Mediterranean trade or transport in the manner of Carthage, Rhodes, Syracuse, or Alexandria. Nor did it command a fabulously fertile hinterland. It enjoyed no natural resources of note except clay, tolerably decent building stone, several small springs, and (we may presume) some quickly depleted timberland. Its hills were defensible but its valleys marshy or flood-prone. In its favor, Rome stood near the middle of the bustling Mediterranean basin at an important intersection of land routes and the Tiber, the largest and most navigable river in the region. This was an important, if hardly decisive, catalyst for the city's rise. The city occupies the lowest viable location for a major settlement in the river basin. Along its final run to the sea, the Tiber's banks are low, unstable, and prone to shifting during heavy floods. The ruins of Ostia, the ancient port town at the river's mouth 25 km below Rome, tell a cautionary tale: it was gradually buried in alluvium over time and its northern district was washed away by the sidewinding current.

Between Ostia and Rome, no bridge could have kept a grip on the river's wandering banks. Only inland – at the cluster of hills by which the world knows Rome – can some stability be found. Here the Capitoline, Palatine, and Aventine Hills are nested around the outer edge of an easterly elbow bend in the Tiber (Fig. 1). River bends tend to amplify into loops over time, but here the barrier of hills thwarts this tendency, providing a short zone of equilibrium that permits bridging. The loop contains a stable island as well, a rarity for the Tiber. Yet the island provides no advantages for a permanent crossing; in fact, the earliest recorded bridges of Rome, the wooden Pons Sublicius and the stone Pons Aemilius, were both downstream from it.

NICHOLAS V'S DECISION TO MOVE THE PAPAL RESIDENCE TO THE VATICAN altered the city's political and cultural landscape. To reflect the new status of the Vatican palace, he enlarged and improved it to serve as his residence, an administrative center for papal business, and a reception space for visiting dignitaries. For defensive reasons he linked it to Castel Sant'Angelo with a wall called the Torrione. His successors further expanded the grounds to include the heights of the Vatican Hill, where Innocent VIII Cibò (1484–1492) later built a small villa, the Belvedere. Julius II linked the palace to the villa with two long wings around a central courtyard designed by Bramante, called the Cortile del Belvedere. Sixtus V divided this in half to house the Sistine Chapel and the Salone Sistina (Fig. 183).

Nicholas V's ministrations to Rome ensured that a citywide surge in palace and church construction would ensue. In fact, the boom lasted 200 years, until the mid-seventeenth century. Colossal palaces such as the Cancelleria and the Palazzo Farnese went up with remarkable speed in the abitato. In the Borgo, too, more important prelates, nobles, and cardinals erected palaces of varying grandeur to be near the center of papal power. For example, Via Alessandrina built by Alexander VI passed alongside one flank of Piazza Scossacavalli, where, with financial inducements to develop the area, two cardinals and a papal chamberlain had all built impressive palaces by about 1520 (Fig. 184). Additionally, Rome's elite undertook to acquire large vineyards and orchards on the intramural hills – but not for their agricultural assets. From the late sixteenth century these productive slopes, favored at last with aqueduct water, were repurposed into luscious villa gardens. The horti of antiquity had returned with a vengeance.

Christendom's most important church was now more than 1,100 years old and probably in physical distress; Nicholas V proposed to demolish it and to build an entirely new basilica. But only in 1505 did Julius II authorize a design competition for a new St. Peter's, which would gradually, after many fits and starts, grow up around its Constantinian ancestor and then, inevitably, consume it.

BY AROUND 400, ROME ALREADY HAD THE BEGINNINGS OF AN AMBIVALENT environmental order, part classical and part medieval. There was a splendid urban frame accompanied by history, legends, and administrative apparatus. The Lateran now headed a system, distinct from the older one but symbiotic with it, comprising a network of parish churches each with its own clergy, and beyond the walls, cemeteries with their own important pilgrimage centers and suburban organisms. Much of this structure was in place by the fifth century.

Rome's imperial religious infrastructure had been largely neutralized: temples were decommissioned; cults suppressed; cult statues moved to public spaces to be regarded simply as art; and treasure, in part at least, removed. A marginal group, the Goths, had settled in Rome on the rundown edges of the Esquiline and Caelian Hills establishing their ecclesiastical tradition, Arianism, a fringe Christian sect considered heretical and often persecuted. The Jews may have been similarly concentrated, probably in the Transtiberim. Meanwhile Mithraism had closed shop and its places of worship had been abandoned or reappropriated for Christian use. The seeds of religious absolutism in a once-tolerant multifaith city were evidenced by the institution of an administrative structure as early as the mid-third century that divided Rome into seven ecclesiastical regions, whereby the Church was now organizing the entire city for its own purposes as if its assumption of civil jurisdiction were only a matter of time.

If Christianity was neutralizing or superseding polytheistic Rome's religious architecture, the same could not be said for the remaining pagan structures, including the imperial centers of government, which still functioned more or less as before. These were the Palatine; the Curia on the Forum and its dependencies, which had been the base of the Senate for a thousand years; and the offices of the urban prefecture, perhaps now in the Basilica of Maxentius, which had absorbed all the once-independent city services including the police, grain and oil distribution centers, and the water and public works commissions. Christian Rome needed this still-functioning administrative network as much as imperial Rome had. The Senate was now more concerned with the city's daily operation than with foreign policy. And since the imperial bureaucracy had left, a skeleton staff oversaw the once-bustling Palatine.

THE BUILT ENVIRONMENT AND NATURAL TOPOGRAPHY OF ST. PETER'S HAVE changed dramatically since the medieval period. There is little left of the grand and ragged splendor of Constantine's basilica, though it survived the vicissitudes of a millennium and more. Nor is much left of the great pilgrimage quarter with the hostels, monasteries, national scholae, the old papal palace, small churches, and diaconiae that crowded the medieval Vatican quarter, known as the Borgo, around St. Peter's basilica. Relics of its physical form are sprinkled in unlikely places: the giant pinecone and peacocks that adorned the central fountain of the atrium now ornament Bramante's Belvedere in the palace grounds. The obelisk, a surviving fixture of Nero's circus, long remained in situ on the south flank of the basilica transept; now it centers Bernini's oval Piazza S. Pietro. Of the other familiar medieval landmarks, only the indestructible Mausoleum of Hadrian is still there (see Fig. 65), demilitarized into a museum and pleasure gardens, and connected to the Borgo by fragments of the Leonine Wall, like some defanged but noble beast on a leash (Fig. 130). Yet despite all the changes, a pilgrim transported from the Middle Ages would have no problem recognizing the pervasive cult of St. Peter and his shrine, the foremost, if not the only, reason for the long, involved development and life of an entire urban region. Few manmade places in the world have more obsessively clung to the sustaining principles of a place of veneration in perpetuity.

To envision the medieval city at the Vatican, the Burgus Sancti Petri, or the Civitas Leonina of the documents, we must do several things: situate Constantine's church in the context of the built and natural environment of antiquity and its subsequent crowning with a string of dependent buildings; examine the development of the Vatican Palace before it was submerged under Renaissance forms; and unearth the urban history of the Borgo itself.

The Vatican and the Lateran were medievalized in distinct ways. For one thing, even if parts of the Vatican were developed under Caligula and Nero and were included in the regionary catalogs, the district retained a suburban character. The emperor Aurelian felt no need to enclose any part of it when he speedily threw up his wall around the city.

THE QUIET REIGN OF FAUSTINA'S HUSBAND, ANTONINUS PIUS (138–161), HAS been characterized, rightly or wrongly, as an Elysium of stability and prosperity. That of his adopted successor, Marcus Aurelius (161–180), troubled by pandemics, barbarian invasions, and economic difficulties, epitomizes crisis and reaction. Yet at Rome, evidence of this contrast – whether drawn from historical accounts, cemetery data, building projects, or inscriptions – is mostly invisible. Under these two Antonine rulers the city suffered few discernible systemic difficulties. Pius built sparingly – his most famous works were temples, one for the deified Hadrian in the Campus Martius and one for his deified wife, and ultimately for himself, on the Forum. Marcus and his son and coemperor Commodus (177–192) built even less; but inscriptions throughout their successive reigns signal a fairly healthy and robust city life. That is not to say that decline did not occur; we simply cannot detect it. And while it is true that Rome was propped up economically with subsidies and other artificial inducements, it would be naïve to presume that a notorious plague that ravaged the empire between about 165 and 180 took no toll here. Nevertheless, the great age of urban expansion was over. Rome would again witness bursts of urban creativity and renewal, but those episodes gradually devolved into a zero-sum game of certain finite physical resources such as water, marble, and granite. By the early fourth century few monumental structures were built without ransacking others.

Some imperial marble quarries were closed during the plague, but the marble yards at Portus and Rome may have been adequately stocked to cushion the blow. Indices of a falloff in building activity we have in abundance: fewer new buildings, fewer dated brick stamps, no new aqueducts for a century after 109. A Trajanic river wharf at the Emporium specializing in building stone seems to have been derelict by the century's end (see Fig. 89). None of these things remotely signals urban decline; Rome had simply reached a saturation point of development. Not coincidentally, for eight decades after 110 there were no citywide fires to whet an emperor's appetite for intervention. It was an appropriate time to take stock. Around 175 or shortly thereafter, Marcus and Commodus expanded the old customs boundary established a century earlier to align it more with Rome's built-up area (see Chapter 13).

AS THE CROW FLIES, ABOUT FIVE KILOMETERS SEPARATE THE VATICAN AND the Lateran – a long walk and a considerable distance on horseback. The spiritual energy flowing between them created an unlikely Christian decumanus, a major east–west street that now rivaled the ancient north–south cardo defined by Via Flaminia/Appia. To the medieval Roman and the foreign pilgrim this was the ultimate ceremonial path, Christian Rome's triumphal way. It conjured images of dazzling processions led by pontiffs and crowned heads of state, eventfully traversing the city with meaningful stops and attendant ritual. Processions such as the papal possesso, a ritual walk to the Lateran taken by the newly crowned pope, began at St. Peter's (Fig. 135). From there one moved down the length of the porticoed Via Cornelia toward the Tiber with the somber bulk of Hadrian's Mausoleum as the first beacon; across Pons Aelius, and through the Campus Martius, with pagan landmarks and Christian stations to the right and left, to the foot of the Capitoline; then skirting it along the north and east to enter the Roman Forum; passing through it to the crest of the Velia at the southeast end, where the Arch of Titus stood and opened the way down the slope to the Colosseum; and up again, to the top of the Caelian and the sprawling and spirited complex of the Lateran.

This was Via Lateranensis, Via Papalis, Via Maior: as close to an organizing central axis as medieval Rome ever had. But it was no triumphal route in the formal sense. Were it not for the power of processions to fashion continuity and cohesiveness through ceremonial movement, it would be seen for what it really was, a string of neighborhoods and a patchwork of streets of different width and indifferent rectitude, going uphill and down, and flanked by everything from rows of unassuming houses or yard walls to the still-proud marble frames of ancient theaters, monumental monasteries, and parish churches. It was no cardo or decumanus in the Roman sense. Via Papalis was not, in other words, the initial organizing determinant of the course of urban order, but the unanticipated and improvised reaction to the pull of two far-flung ceremonial centers.

AUGUSTUS’ SUCCESSOR, TIBERIUS (14–37 C.E.), SPONSORED ONLY A FEW urban developments in Rome, the most significant being the expansion of the imperial Palatine compound into the Domus Tiberiana, a genuine palace designed to accommodate the growing imperial entourage, especially the Praetorian Guard. Other cohorts of the guard were quartered in a full-scale military camp, the Castra Praetoria, just northeast of the Servian Wall; this was later nested into the Aurelian Wall (see Fig. 80). Caligula (37–41) launched several aggressive building campaigns, some of which died prematurely with their patron. Others were completed by his successors. Claudius (41–54) focused on infrastructure rather than the city's monumental core. The splendid Porta Maggiore, doubling as an aqueduct arcade and a city gate, is his most enduring monument in Rome (Fig. 38). Over it flowed his two great aqueducts, one channel stacked upon the other: the Aqua Claudia and the Anio Novus above, both begun by Caligula. Their arcade of solid peperino stone still dominates the landscape east of the city. Together they augmented the existing water supply by as much as 40 percent. Claudius devised no known monumental baths, water play, or naumachia to justify or advertise them. Yet combined, Frontinus later tells us, the two lines were supplying all 14 city regions from 92 distribution tanks in his time (ca. 97 C.E.). In number, these tanks constituted 37 percent of the total urban network, and in volume 34 percent; the total brought in an astounding (but in Frontinus’ opinion, scandalously underperforming) 333 million liters per day.

This precious glimpse of Rome's “soft” structure at one moment in its history says little about its “hard” aspect, however. After Augustus, the first traceable and truly systemic changes to the urban fabric belonged to Nero (54–68), who took concrete vaulted architecture not only to new heights of creativity, but also into mass production. The central-Italian preference for concrete as a monumental building material developed slowly and incrementally. Writing early in Augustus’ reign, Vitruvius provided a simple formula for this miraculous slurry that hardened into veritable stone, far stronger than any mortar. Its key ingredients were chunks of stone aggregate and a matrix of water, slaked lime, and pozzolana – a volcanic sand that gives concrete its extraordinary strength.

PIUS IX AND KING VITTORIO EMANUELE II BOTH DIED IN 1878. QUIETLY interred at St. Peter's, Pius was largely unmourned while the king received a hero's burial at the Pantheon. Almost immediately, a national monument embodying the aspirations and intentions of the new nation was proposed in his honor. The still-unratified 1873 master plan had not anticipated such a monument, so the contentious task to choose a site remained. After several false starts, a design was selected to crown the symbolically potent Capitoline Hill facing Palazzo Venezia. In the abstract, the monument, known as the Altare della Patria, the Altar of the Fatherland, enjoyed wide popularity. Yet once construction began in 1885 the shock of its gargantuan size, bright white surfaces, inappropriate site, and disregard for the urban fabric stirred resentment. Cultural critics delighted in vilifying it long before its inauguration on 4 June 1911, the 50th anniversary of Italian unification. Quite apart from its aesthetic extremes, it was jammed too tightly into the medieval and Renaissance neighborhoods surrounding the hill, narrowing local streets and exacerbating traffic just as motorized transit was beginning to burden the city's infrastructure (Fig. 212). And it set in motion actions and reactions with far-reaching consequences. Traffic was diverted around it, and this entailed a complete rearrangement of Piazza Venezia, which now functioned as a prologue to the monument, and became, along with the Palazzo Venezia on its west side, the “ritual nucleus” of modern Rome.

During the liberal administration of Mayor Ernesto Nathan, a new piano regolatore was ratified in 1909. Called the Sanjust Plan after its developer, Edmondo Sanjust di Teulada, it focused, as did earlier plans, on traffic intervention. But there were important innovations, too. Its new planning area, enclosed by a proposed urban expansion ring road, included the Roman Campagna immediately outside the walls; it displayed topographic contours for the first time; it expanded and defined new public transit lines; it described a rudimentary zoning plan with three types of housing, fabricanti (multifamily midrise), villini (low-rise), and giardini (luxury garden residences) linked to specific neighborhood development plans; and it identified specific locations for public parks and open space (Fig. 213).

WHEN THE BYZANTINE EMPIRE CEDED CONTROL OVER THE PAPACY IN 752, the Church, now protected by the Franks, became a vassal of the Carolingian dynasty. Charlemagne, first as king (768–814) and then as Holy Roman Emperor (800–814), and Popes Hadrian I and Leo III joined in a relatively stable alliance. Meanwhile, ties between the Church and the Byzantine rulers unraveled in the mid-ninth century as threats from outside invaders such as the Lombards and Saracens increased. The Church and the Holy Roman Empire coexisted uneasily for more than five centuries, with the emperor most often dominating. The growing Roman noble class, itself divided into ruthless factions, sometimes supported the pope and at other times the emperor.

This led to several important changes. The continued Saracen peril on the seas spelled the end of the port facilities at Ostia and Portus, and their abandonment resulted in some new, smaller river ports to augment those already within the city. The exposed countryside contained treasures, both material and spiritual, that had to be moved within the wall for safekeeping or given their own local protection. Relics of martyrs and other Christians, hitherto inviolable where they lay, were now dug up and taken into the city, where they were distributed among the churches. At the same time, the great shrines were fortified. The fort of Johannipolis around the complex of S. Paolo and the Leonine Walls of the Borgo were the work of the ninth century. In the Roman countryside both the castle and the fortified village (both called castellum) had become common. The population shifted markedly to new defensible centers and the domus cultae broke up. The once tightly administered papal domain, a vast landholding operation strapped to the Lateran, splintered into fragments ruled by individual churches, monasteries, and increasingly the rising noble families. The same pattern of breaking up large units into smaller governable – that is, defensible – elements transformed the urban landscape as these families, for protection, engaged their own private gangs for open warfare in the streets.

But by the early tenth century one powerful family – the Tuscolani from ancient Tusculum southeast of Rome – effectively seized Rome and took control of the Church. We first hear of them in the person of Theophylact I (d. 924/5), count of Tusculum.

THE NAME “COLOSSEUM” IS OF MEDIEVAL ORIGIN, REFERRING SIMPLY TO the amphitheater by the Colossus – a towering gilded bronze statue, more than 30 meters high, of Sol, the sun god. Originally erected farther west, in an entrance court of the Domus Aurea, it began as a nude portrait statue of Nero. This identity could not be allowed to stand, and probably under Vespasian (69–79) it acquired the more generic features of Sol. Yet Sol was an exotic import with little devotional value in Italy. Evidently the statue was saved because it was an object of awe – a monument worthy of the caput mundi, the head of the world, supplanting the long-collapsed colossal sun god of Rhodes among the world's wonders. Hadrian later had it moved at great expense to its place near the amphitheater.

Founder of the new Flavian dynasty, Vespasian confronted a delicate ideological task. It was not enough to put a new face on a statue; the city itself needed somehow to shed its Neronian identity without needlessly destroying Nero's genuine achievements. The amphitheater was a hedge of sorts. Its introduction constituted a symbolic erasure and emendation, but it was also a building of high public value replacing an inessential amenity. Another monument nearby, the baths later completed by his son, Titus, who would succeed Vespasian as emperor (79–81), also contributed to this campaign. The baths occupied a decommissioned sector of the Domus Aurea, yet they were consciously modeled on Nero's splendid prototype in the Campus Martius. Their most original feature was a gargantuan covered stairway thrust out from the slope almost up against the Colosseum (Fig. 46). Broad and hulking, it was a veritable cartoon of public accessibility, like the monument to Vittorio Emanuele II on the Capitoline Hill today. Whether or not inspired by some precedent, it was clearly intended as an ostentatious declaration: this place benefits and belongs to everyone.

Vespasian's priority was to break with Nero's cult of personality while emphasizing the continuity of traditional institutions in Rome. In the heart of the city, he achieved this with projects at opposite extremes of the Forum valley. The most urgent task lay at the northwest end, on the summit of the Capitoline Hill.

LET US PAUSE TO PONDER THE REMOTENESS OF ANCIENT ROME FROM OUR own urban experience. In the imperial period it was a city of unprecedented scale and complexity supporting about a million people. It had an incomparable infrastructure of roads, aqueducts, and sewers. Its supply systems and administrative apparatus were the most sophisticated in the ancient world. But if we contemplate the ancient city from our own urban experience, we see that it had no mayor, city council, or city hall; no urban planning commission; no sanitation department or public health service; no hospitals, public schools, or public transportation; no homeless shelters; no police crime units to prevent or investigate wrongdoing; and no prisons. (The famous carcer was merely a holding cell for condemned political prisoners.)

During the republic, Rome relied heavily on its citizenry to maintain infrastructure, uphold public order, and provide social amenities according to a patchwork code of laws and expectations. Outside this limited domain of private duty or initiative, the task of improving or maintaining the city fell mainly to the censors and the aediles, elected short-term magistrates whose most fundamental duty was to oversee public morals. Often the two censors undertook major public building and infrastructure projects of a nonsacred nature, while the two (later four) aediles saw to the city's maintenance, the proper execution of games, and the enforcement of personal modesty and restraint in public building. Their role was genuinely practical but also symbolic; the state of the urbs reflected their personal moral standing. The aedileship retained this signification long after the censorship lapsed, as was demonstrated when the emperor Caligula, observing that some streets of Rome were unswept, ordered mud to be thrown onto the toga of Vespasian, who was an aedile at the time.

Prodded by various crises, Rome did develop a robust professional bureaucracy in the high empire, some of it publicly and some imperially financed. In one unique case, the water commission's staff was divided between 240 public and 460 imperial slaves, the latter contingent added by Claudius. The city kept extensive records in a variety of locales: maps of publicly owned property at the Atrium Libertatis, death records at the grove of Venus Libitina, imperial procuratorial archives at the Horrea Piperataria (those incinerated in 192), etc.

ARTISTS AND ARCHITECTS HAD FOLLOWED THEIR INSPIRATIONAL COMPASSES to Rome for centuries, but in the sixteenth century they began arriving in droves from all over Italy and Europe. With sketchbooks in hand, they came to study – and draw, paint, or etch seemingly every antiquity, palace, piazza, and bend in the Tiber River. The city was their subject – its buildings, ruins, topography, and people (Fig. 198).

After the Thirty Years War ended in 1648, when European travel became easier and safer, Italy enjoyed a more or less permanent surge of cultural tourism. For gentlemen of rank, particularly those from Great Britain, an extended period of European travel known as the Grand Tour, taking many months and sometimes years, was expected. The tour rapidly became a social and educational phenomenon – a kind of peripatetic finishing school in the gentleman's cultural education, culminating in Rome. King Louis XIV established the French Academy in 1666 so that artists and architects could measure and draw classical Rome as a foundation for their own contemporary practices. (Other nations followed only in the nineteenth century.) Although no longer a political force in Europe by the mid-seventeenth century, the city, with its fantastic mix of ancient relics and Renaissance buildings, still held allure and provided the excuse for educative travel – a new kind of pilgrimage, intellectual and aesthetic rather than religious, that Europe's burgeoning Protestant elites could embrace, and that could profit Romans catering to them.

Now the need to feed, quarter, and entertain distinguished visitors in suitable style, and to accommodate the vast retinues of servants and horses they had with them, acquired even greater urgency. The area at the foot of the Spanish Steps quickly became identified with the foreigners who tended to settle or sojourn there, particularly the British. Also, the need arose to respond to the visitors’ growing appetite to collect mementos, whether ancient sculpture or contemporary painted and printed views of the city and the Campagna (Fig. 199). Their lust for loot found a ready market, and the cultural tourists returned home with crate loads of antiquities and images of Rome's ancient and modern attractions.

IN NO OTHER CITY OF THE EMPIRE DID THE IDEA OF ROMAN GOVERNMENT survive as tenaciously as in Rome itself. Two symbolic aspects sustained this idea: the concept of imperium, the privilege of continuing Roman imperial rule; and the counterpoint of populism, the trappings of a people's government, the Roman Comune, as contained in the rubric Senatus Populusque Romanus, or SPQR, stamped to this day on every length of pipe and sewer tube laid by the municipality. The Palatine was the physical location for the institutionalization of the concept of imperium during the Christian Middle Ages, and the Capitoline became the new home of the Roman Senate in the eighth century.

Of all the features that characterized Rome as the quintessential imperial city of classical antiquity, the Palatine was preeminent; it served as residence of the court and headquarters of the large and mighty imperial bureaucracy. If the imperial domain was readily transferable to the Church (as we have seen with large land grants), this was not the case for the Palatine, which as official residence of the emperor was managed by the Senate, as were the other major monuments of the ancient city. The Palatine was the symbol of imperial authority, the memoria of imperium, as it were, and was certainly not conveyable without admitting that the West was lost to the Byzantine Crown. Whether or not the Roman emperor, resident in Constantinople, ever saw the Palatine, it remained his premier palace up to the collapse of the Byzantine Exarchate in 752, when all pretense of holding the West ended.

Under the emperor Justin I (518–527), an office was created of three curatores carrying the highest title of illustris, who took charge of all imperial residences, including the Palatine. Later the office was decentralized and the number of curatores increased so that every palace had its own maintenance endowment and probably its own curator. A letter of Gregory the Great attests to the existence of “diverse Palatine officials in Rome.” The palace was functional at least until the early eighth century. The emperor Constans II stayed at the palace in 663 and it remained functional until at least 712, when the dux Christophorus resided there.

THE NEWLY WALLED CITY WAS A RAGGED THOUSAND-ACRE QUILT OF medium-density development patched about by sacred groves, sanctuaries, and tracts of suburban farms that would later be absorbed into horti, great aristocratic garden estates (see Chapter 11). Most of its area, hosting perhaps 40,000 residents in all, was subdivided into four large regions, each corresponding to an urban tribe of citizens: Subura, Esquilina, Collina, Palatina. Westward lay the lonely extramural expanse of the Campus Martius – “Field of Mars.” Its only man-made precinct was the Villa Publica, where at a venerable altar of the war god, the Ara Martis, the general census was periodically taken and soldiers were conscribed. In time, the magistrates overseeing these duties, the censors, would also come to dominate secular construction in Rome.

The fourth century B.C.E. witnessed profound changes in Roman social and political life, mostly along two intertwined paths: proletarization and militarization. Against fierce patrician opposition, the plebeians won the right to hold Rome's premier magistracy, the consulship, in 367. To mark the uneasy class realignment a new goddess was contrived in the abstract, allegorical manner characteristic of the Greeks: Concordia. Her temple was built on the Forum's northwestern rise, perched watchfully over the people's Comitium and the Curia, or Senate house, adjoining it (Fig. 11). Henceforth former consuls of both classes would erect temples at Rome. As military commanders, they conventionally vowed a new temple to a tutelary god while on campaign. If victorious, they fulfilled the vow (votum) at Rome afterward from the proceeds of war spoils. Temples of this sort are called votive.

Roman success in the Samnite Wars of the second half of the fourth century precipitated a flurry of victory temples back home. By 270 Rome controlled peninsular Italy, and the consequent influx of slaves had swelled the city's population to as much as 200,000. The dedication of votive temples was in full spate (Fig. 12). New kinds of war monuments emerged as well. In 338, the conqueror of the Latins, the plebeian Gaius Maenius, celebrated Rome's first naval victory by mounting a speaker's platform on one side of the Comitium. Perhaps from the very start it bristled with the bronze battering rams of ships Maenius had conquered. Called the Rostra (“beaks”), this platform and later imitations would become fixtures of Roman forensic politics.

THE FIRE OF 80 CUT RIGHT ACROSS THE CITY'S MONUMENTAL CENTER FROM the Palatine Hill westward to the heart of the Campus Martius. The omission of secondary neighborhoods from admittedly sketchy surviving accounts may be merely prejudicial, but we can at least allow that Nero's residential building regulations did some good. Still, the list of high-value architectural casualties is long (Fig. 55). Titus had barely begun repairs before his death in September 81. The city's refashioning would belong to Domitian.

Domitian set about not just repairing or replacing, but augmenting. His architect, Rabirius, devised an entirely new scheme for the residential core of the palace on the southern and eastern Palatine, though we have no evidence that the fire touched this area. In its baroque intricacy and fecundity of volumetric ideas, with its banquet halls, baths, sunken gardens, and elaborate engagement with the Circus Maximus below, the palace became the new beacon of the Roman architectural revolution, outshining the fast-disappearing Domus Aurea (Fig. 56). Obsessively and redundantly, Domitian built monuments to his family: the temple of Vespasian and Titus and the Arch of Titus on the Forum; the Temple of the Flavian Family at his own birthplace on the Quirinal; and the Porticus Divorum, a large enclosure in the Campus Martius on the traditional site where the census was taken and soldiers were conscribed, again honoring his deified father and brother. Following long-standing custom, he was fond of anchoring memorials to events in the urban landscape.

If these dynastic monuments convey insecurity and megalomania in equal measure, Domitian can at least be excused for scrupulously appeasing the gods whose temples had been ravaged in Rome during his lifetime. In the city he dedicated another series of fixtures anchored in the landscape: “altars of the Fire of Nero,” which had been vowed after 64 but never built. The inscription of one altar obliquely chastises Nero's negligence, implying that the fires of 69 and 80 resulted from his impiety. The emperor lavished special attention on Jupiter, whose temple – the Capitolium – had suffered from both calamities.