Koch’s postulates originally proposed a one microorganism–one disease approach to disease; however, it is now clear that many diseases of plants and animals are associated with changes in the taxonomic composition and function of the microbiome, and that health and disease are mediated by a dynamic interplay between host factors, environmental factors, the host microbiota and pathogenic microorganisms. Commensal microbes can become pathogenic under certain conditions, and disease can arise from complex polymicrobial infections. Although causation and correlation can be difficult to untangle, it is clear that the host microbiome plays a key role in resisting colonisation by pathogens across all host taxa, from plants to animals to humans. This offers exciting possibilities for manipulating microbiomes in order to reduce pathogenic infection in a range of contexts, including agriculture, wildlife and human health, through the use of probiotics, prebiotics and microbiome transplants, among other approaches.

A classic example of microbiome function is its role in nutrient assimilation in both plants and animals, but other less obvious roles are becoming more apparent, particularly in terms of driving infectious and non-infectious disease outcomes and influencing host behaviour. However, numerous biotic and abiotic factors influence the composition of these communities, and host microbiomes can be susceptible to environmental change. How microbial communities will be altered by, and mitigate, the rapid environmental change we can expect in the next few decades remain to be seen. That said, given the enormous range of functional diversity conferred by microbes, there is currently something of a revolution in microbial bioengineering and biotechnology in order to address real-world problems including human and wildlife disease and crop and biofuel production. All of these concepts are explored in further detail throughout the book.

Antiquity

Since we have no literary references to the Schola Xanthi (Figs. 0.3–4, 1.3, 8.9–10, 16.1–5), our reconstruction of its early history is largely conjectural. Possibly Augustan or erected during the construction of the Arch of Tiberius and the Temple of Concord, it was remodeled when Titus and Domitian built the Temple of Vespasian, and, finally, while Septimius Severus was putting up his adjacent arch, it was again redone. After antiquity, the site disappeared under the rubble that covered the west end of the Forum, and our only information on it comes from documents that relate the history of the little Church of Saints Sergius and Bacchus (built c. 685 CE, destroyed c. 1575). Near the Arch of Severus, the church faced the Forum, its apse not far from the three surviving columns of the Temple of Vespasian.

Prologue: The Republican Forum (508–31)

Established as a meeting place for the inhabitants of the adjacent, previously independent villages, the Republican Forum occupied an irregularly shaped, marshy valley below the Palatine and Capitoline Hills. Reclaiming the central marsh by massive earth fills in the late sixth century, its builders initiated the continuous evolutionary changes that, in the next five centuries (c. 525–44), transformed the site into the Forum of the late Republic. Literary tradition credited the Temple of Vesta at the southeast end of the valley to Rome’s second king, Numa Pompilius (715–673), who had erected it next to the Regia, his own residence. At the northwest end, Pompilius’ successor, Tullius Hostilius (672–641), built the Curia Hostilia, the Senate House named after him, and, in front of it, the Comitium, the outdoor meeting place for Rome’s popular assemblies. At the end of the sixth and the beginning of the fifth centuries, the early republican Temples of Saturn and Castor went up to the south, and, by the fourth century, a line of aristocratic dwellings connected these temples and defined the edges of the piazza (Fig. 1.1).

During the course of the second century, two rectangular basilicas replaced many of these houses. On the north side of the Forum stood the Basilica Fulvia (later called Aemilia), and to the south, the Basilica Sempronia. In the late second century, a temple to Concord on the northwest side of the Forum commemorated an aristocratic victory over the people, and by early in the next century (after 78), the monumental facade of the Tabularium, with its impressive second-story arcade and engaged Doric Order (Figs. 11.1, 2, 6, 9, 10, 21.21), hid the slope of the Capitoline Hill.

The Late Republic and Empire

By the late Republic, the West Rostra, the structure from which speakers addressed the people, flanked by statues of Pythagoras and Alcibiades, was incorporated into the seating area (the Comitium) immediately in front of the old Senate House, the Curia Hostilia, a site buried today under the Church of Saints Martina and Luke (Fig 1.1). Before his assassination, Caesar had started a new Curia aligned with the colonnade on the south side of his Forum, and, at right angles to it and just west of it, he built a new rostra (Figs. 8.4–5). The space on Caesar’s Rostra was limited, but Augustus gradually enlarged it between 42 and 12 BCE. While repeating the general plan and decorations of its predecessor, Augustus’ Rostra was much larger. Flavian repairs (69–96 CE) strengthened an upper platform now crowded with heavy honorary statues and their pedestals. But in the reign of Septimius Severus (193–211), five massive new honorary columns erected at the back of the podium required heavy foundations (Figs. 8.1–2, 10–12), and, in the fifth century CE, a concrete brick-faced concrete addition, the so-called Vandalic Rostra, extended the front of the older platform farther north.

The Early Republic

Located close to the Shrine of Vesta (Figs. 0.1, 18.2, 20.1), the Temple of Castor and Pollux (famous and important deities throughout Roman history) was the largest sacred structure in the Forum and, in all periods, one of its most important centers. It dated from the early fifth century BCE, and tradition connected it with a famous Roman victory over Rome’s neighbors, the Latins, near Lake Regillus, fourteen miles from Rome, just north of Frascati. In this crucial battle for Rome’s safety, the Latins had sided with the ousted king of Rome, who had been expelled some years earlier. In the prosaic account by the Roman historian Livy, the battle was long and hard. Finally, hoping for divine help, the Roman commander, Aulus Postumius, vowed a temple to Castor and Pollux and promised rewards to the first and second soldiers to enter the Latin camp. Thus encouraged, his forces bested the Latins. But, for the more credulous, there was a famous legend about the battle and its aftermath.

As the Roman cavalry (the equites) charged the Latins, two extraordinarily handsome young men on horses appeared. Leading the charge, they drove the helpless Latins before them. When the Romans had captured the Latin camp, the two appeared again at the Spring of Juturna near the Temple of Vesta in the Roman Forum. By the disorder of their clothes and the sweat on their steeds, they appeared to have been fighting, and, after they had watered their steeds, the Romans gathered around to ask news of the battle with the Latins. The youths described the fight and reported the Roman victory. Then, vanishing from the Forum, they were never seen again. The next day, when a letter from Postumius arrived with news of the Roman victory, the Romans realized the two handsome strangers were the gods Castor and Pollux, the children of Zeus and Leda, and accepted Postumius’ vow for a temple in their honor. Postumius died before completing the temple, but, some years later, his son dedicated it on July 15, 484/483, the anniversary of the famous battle.

Saturn in Early Rome

For modern scholars, Saturn (Fig. 13.2) was a Sabine agricultural deity originally from Sicily. His name and shrine had once dominated the Capitoline Hill. Rome’s late Etruscan kings purportedly banished him from its summit, but his cult survived, and from Rome’s Etruscan overlords, the god took on the darker, bloodier, more ominous character associated with human sacrifices and their later survival in traditional gladiatorial games held annually in December. By the end of the first century BCE, learned writers identified Saturn with the remote ages prior to the foundation of Rome. Before the war with Troy, a “Greek expedition” with “a small Trojan element” had followed Hercules into Italy and “built a town on a suitable hill…now called the Capitoline Hill, but by the men of that time, the Saturnian Hill or, in Greek, the hill of Cronus.”

Locating a “Saturnian Gate” behind the Temple of Saturn on the Clivus Capitolinus that led to the top of the hill, Varro called this venerable Capitoline settlement “Saturnia.” Its inhabitants (or perhaps other Greeks) “erected the altar to Saturn which remains to this day [the first century BCE] at the foot of the hill near the ascent that leads from the Forum to the Capitol, and it was they who instituted the sacrifi ce which the Romans still performed even in my time observing the Greek ritual.” Later imperial writers perpetuated and revised the memories of these antiquities.

The cult statue in the cella must have represented Saturn as he appears on late republican denarii: a mature bearded man with flowing hair bound with a fillet ( Fig. 13.2 ). The statue would have been colossal with an internal framework. An internal oil reservoir (or reservoirs) lubricated the ivory face and bare body parts. The vestments may have been of gilded wood. The statue’s crimson veil may have been of real fabric, and its scythe of wood and metal. A second image kept in the temple was carried in processions, and this image and/or the cult statue was “bound during the year with a woolen bond, and is released on his [Saturn’s] festal day,” December 17, the fi rst day of the nearly week-long Saturnalia, a festival that symbolized Saturn’s role as the divine patron of liberation.

The Republic

Roman tradition credited the vow to build the Temple of Concord to Marcus Furius Camillus, dictator, conqueror of the Etruscans. In the midst of the plebeian fight to obtain admission to the consulship from the patricians in 367 BCE, “turning to the Capitol, he [Camillus] prayed the gods to bring the present tumults to their happiest end, solemnly vowing to build a temple to Concord when the confusion was over.” According to the poet Ovid, “he kept his vow,” but archaeological remains of this early monument have been difficult to identify, and it may not have been built after all. Indeed, the first shrine to Concord on the site seems to have been founded by Gnaeus Flavius, a curule aedile, the son of a former slave, despised by the patricians for his humble origins and popular measures.

The Augustan Forum

Augustus, as we have seen, continued Caesar’s projects and had, by the end of his reign (14 CE), totally rebuilt the Forum (Figs. 21.2, 21). Beginning with the Temple of Caesar (dedicated in 29 BCE), he ended by sponsoring Tiberius’ reconstruction of the Temple of Concord (dedicated in 6 CE). This work concluded centuries of piecemeal change: new buildings and monuments that related only incidentally to one another and to the architecture of the Forum as a whole. In contrast, the design, materials, and detailing of Augustus’ structures were the homogenous products of local craftsmen and numerous imported, highly experienced Hellenistic artisans. Enormous in scale, crafted from local materials and Italian and foreign marbles, superbly finished and detailed, they recalled, equaled, and even surpassed the structures in the great urban centers of the Greek East. Components of a single design, worked out gradually over three and a half decades, they all displayed four distinguishing characteristics: purpose, siting, design, and decoration.

Purpose

Augustus and his associates evidently considered the existing state of the Forum inviolable. That is, they generally did not demolish extant structures to erect substitutes. The Temple of Caesar, the new flanking arches, and Augustus’ enlargement of Caesar’s West Rostra marked the major exceptions to this rule (Figs. 0.3–4, 8.1–2). But for the temple, popular demand after Caesar’s assassination had already sanctioned a memorial column on the site, and the triumvirs who had preceded Augustus’ rise to power (and included Augustus himself) had decided on a new shrine. Indeed, for a youthful autocrat whose initial claim to power rested on the success and prestige of his adoptive father, deification of and a temple to that father were a political necessity. For the decorative arches that flanked the temple – the Parthian Arch on the south, the Arch of Lucius Caesar on the north (Figs. 0.3, 1.2) – major political and dynastic achievements, diplomatic success abroad (the Parthian Arch), and the promise of future dynastic stability at home (the Arch of Lucius Caesar) offered acceptable reasons. And, for Augustus’ enlargement of Caesar’s Rostra (Figs. 0.4, 1.3), a need for more space is probably the best explanation.

Varus

The Arch of Tiberius (Figs. 0.3–4, 1.3, 8.9–12, 15.1–6, 21.22–26) was connected with one of the most terrible disasters of the reign of Augustus. By 9 CE, the Romans were beginning to expand in Germany. In 6 or 7, Augustus appointed Publius Quinctilius Varus, a member of the imperial family by marriage, as governor. Varus had enjoyed a long and successful political career including governorships in Africa (8–7) and Syria (7–4). In 6–7, Tiberius, Augustus’ adopted son and heir, was still fighting in nearby Pannonia, but Germany was relatively peaceful. With three legions, Varus marched through the partially pacified zone between the Rhine and the Elbe introducing the inhabitants both to Roman power and to the Roman administrative system. Described as placid in mind and body, he was reputed to be more accustomed to life in the camps than to campaigning. In endless legal proceedings, he behaved more like a “city praetor” than a general in command of an army in hostile German territory. Worse yet, treating the Germans like slaves, he exacted money from them.

A revolt was inevitable, and its potential leader, Arminius, shared Varus’ mess, seeming so friendly that Varus suspected nothing. At the last banquet before the beginning of hostilities (9), Segestes, a local chieftain and Arminius’ rival, urged Varus to arrest Arminius and his friends. If they were in Roman custody, he assured Varus, their leaderless followers would be immobilized. Varus could sort the whole matter out later. Varus, however, refused to listen to any accusations against his friend. Indeed, on Arminius’ advice, he broke up the Roman army into small local units that posted to police duties throughout the province

The Curia Hostilia

According to Livy, Romulus (771–717 BCE), Rome’s legendary founder, established the Senate, originally a royal advisory council of a hundred men, the heads of the noble clans (patres) whose descendants became Rome’s aristocracy (the patricians). Where the Senate held its sessions in the early decades of its existence is unknown. Eventually, using war booty from the conquest of the neighboring Latin town of Alba Longa, King Tullius Hostilus (672–641) brought the Alban aristocrats to Rome and, for his newly enlarged Senate, built a “meeting house,” a Curia (Fig. 1.1), on the northwest side of the Forum just north of and adjacent to the voting area (the Comitium) for Rome’s earliest popular assembly, the comitia curiata. Like the surviving building, this Curia, “which,” says Livy, “continued to be called the Curia Hostilia as late as the time of our own fathers,” was a rectangular structure with a wooden roof that was formally considered a temple. Oriented to the cardinal points, its south entrance opened directly into the Comitium, an area enclosed by rows of seats that served as the Curia’s steps. Major historical paintings decorated the interior. The one installed in 363 by M. Valerius Messala commemorated his Sicilian victory over King Hiero of Syracuse and the Carthaginians during the First Punic War.