Campus Martius

• 1. Introduction

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  Campus Martius, the Field of Mars, sits at the heart of one of history's most layered cities. In 1581, the French essayist Michel de Montaigne walked through Rome and made a striking observation: the old streets lay more than thirty feet below the level of those then in existence. The ancient city had not been erased; it had been buried, built over, century by century, by the very people who inherited its ruins. Campus Martius is the place where that process played out most dramatically. What began as an open plain outside Rome's sacred boundary became a parade ground, then a construction site for temples and theaters, then the most populous neighborhood in medieval Europe, and finally the dense urban core of modern Rome. How did a marshy field sacred to a god of war end up as the beating heart of a great city? The answer runs through myths of drowning twins, the political ambitions of Roman generals, the fall of aqueducts, and a pope who built a road in the sixteenth century.

• 2. Sacred Ground

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  Mars was among the most significant gods in the Roman pantheon, patron of both military endeavor and agriculture. The month of March bore his name, and until 153 BC, March also marked when consuls began their work. The field outside Rome's pomerium, the sacred boundary of the city, was linked to Mars through the Ara Martis, an altar mentioned in sources going back to the eighth century BC, though no one knows exactly when it was built or when it vanished.

  Rome's founding myth wove the Campus into the city's deepest story. Rhea Silvia's twin sons, Romulus and Remus, were cast into a swelling Tiber River, which would later run along the western boundary of this very land. After washing ashore downstream and eventually founding Rome, Romulus ruled as the city's sole king until a storm cloud descended upon the center of the open field to carry the elderly king to the afterlife.

  When Rome's last Etruscan king, Tarquinius Superbus, was defeated and exiled, the plain between the city and the river was dedicated formally to Mars. Roman men assembled there each spring before heading off to fight the hostile tribes surrounding early Rome. Citizens gathered for major religious festivals. For centuries, a small altar to Mars near the field's center was the only visible structure. The first real change came in 435 BC, when the Villa Publica was established in a prepared three-hundred-meter clearing, giving citizens a place to be counted in the census every five years. No permanent structures followed for another two centuries.

  The Campus also hosted rituals that mixed blood and spectacle. On the fifteenth of October, a festival called the October Horse drew crowds for chariot races; the winning horse was sacrificed to Mars, and its severed head was decorated with leaves. This tradition, said to have started in the sixth century BC, was meant to protect the coming year's crops and the soldiers returning from campaigns.

• 3. A Field Fills With Monuments

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  The Punic Wars changed everything. As Roman military expansion pushed out of the Italian peninsula in the mid-third century BC, seasonal musters on the field became less common. But the wars brought enormous wealth into Rome, and generals who had sworn vows to deities began funding temples to honor those promises. Wooden markets and entertainment venues appeared alongside the temples, though many were designed to be temporary.

  The Hellenistic age, following the death of Alexander the Great in 324 BC, sent a wave of building ambition through Rome. Seven temples rose in the Campus Martius during this period, including the Temple of Bellona in 296 BC, the Temple of Fortuna in 293 BC, and the Temple of Hercules in 221 BC. Stone architecture replaced the older, coarser building methods. Ground plans grew mathematically complex, and the aesthetic refinement of Hellenistic design left its mark on everything built during this era.

  By 55 BC, Pompey constructed the Theatrum Pompeium, the first permanent stone theater in all of Rome. When the Curia Hostilia burned down in 52 BC, the Senate sometimes gathered in that theater instead. Julius Caesar planned for election enclosures called the Saepta to be placed in the Campus; his heir Augustus completed them. In 33 BC, Octavian dedicated the Porticus Octaviae, built from spoils of the Roman-Dalmatian War.

  Starting in the time of Sulla, building lots were sold or granted to influential Romans, and apartment blocks and villas began pressing in on what had been common land. The field that once mustered armies was becoming, piece by piece, a city.

• 4. Augustus Reshapes the Field

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  Marcus Agrippa, one of Augustus's closest allies, transformed a stretch of swampy Campus Martius ground into parkland, pools, and baths, the complex known as the Laconicum Sudatorium or Baths of Agrippa. Agrippa also built the Porticus Argonautarum and the original Pantheon, later rebuilt by Hadrian in the form still standing today. In 19 BC, Agrippa completed the Aqua Virgo to supply water to the new baths and fountains.

  The ancient historian Strabo described the scene in terms that read almost like wonder: the Campus afforded space simultaneously for chariot races, equestrian exercises, ball-playing, hoop-trundling, and wrestling, all without interference. The ground was covered with grass throughout the year. The hills above the river presented what Strabo called "the appearance of a stage-painting." Because the Romans considered this the holiest of places, he noted, they buried their most illustrious men and women there. The Mausoleum of Augustus, a great mound near the river on a lofty foundation of white marble, sat in the northern, less populated part of the field. A bronze image of Augustus stood on top.

  The Saepta Julia, designed to manage crowds at elections and prevent fraud, was the first Campus building closely associated with Augustus. Agrippa completed and dedicated it in honor of Augustus. The Pantheon, finished within a year of the Saepta Julia, served pre-election functions. Agrippa attempted to name the Pantheon after Augustus but was refused; instead, he placed statues of Augustus, Julius Caesar, and himself in the porch, permanently linking the building to all three men.

  The Ara Pacis, the Altar of Peace, embodied Augustus's broader message. Begun in 13 BCE and dedicated in 9 BCE on Livia's birthday, its four carved panels formed a visual argument. The south panel showed Augustus, Agrippa, Livia, Tiberius, and other members of the Augustan family in procession. The north panel showed the Senate walking alongside Augustus rather than against him. The east panel depicted Tellus, goddess of earth and peace. The west panel showed either Aeneas or Numa Pompilius performing a sacrifice. Together, the panels promised peace, fertility, and permanence.

• 5. Emperors and Decay

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  Hadrian and the Antonine emperors continued the tradition Augustus had established, framing imperial rule through construction. In 119 AD, a temple to Hadrian's mother-in-law, the Divine Matidia, was added. Antoninus Pius later built a temple to Hadrian himself. The Severan emperors, by contrast, put little into the Campus Martius; the space was already crowded, and their building energy went elsewhere in the capital.

  After the great fire of 64 AD, Domitian rebuilt the burned monuments and added a stadium that eventually became today's Piazza Navona, along with an odeion, a small performance hall. Domitian also renovated the Horologium Augusti, the solar instrument linked to the obelisk originally set up under Augustus. Scholars now understand that instrument not as a sundial, as was assumed before the 1980s, but as a solar meridian, designed to track the length of days and nights and check the civil calendar against the solar year. The fact that Domitian chose to renovate rather than replace it kept the site dedicated to Augustus even into a later reign.

  By the mid-fourth century, when Constantius II visited Rome, many pagan temples had been closed. Buildings dedicated to Christianity began taking over their spaces. Some structures were reduced to raw material; marble facings and columns were burned into lime powder for reuse. Three earthquakes struck the city between 408 and 508 AD. Two floods washed over the low-lying Campus in 398 and 411 AD. The Visigoths sacked Rome in 410 AD; the Vandals followed in 455 AD. In 663 AD, the Pantheon's bronze roof tiles were removed and replaced with lead, an act a writer named Gregorius described as the result of excessive greed for gold.

• 6. The Medieval City

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  When barbarian invasions cut the aqueducts feeding Rome's hilltop neighborhoods, the population did what populations do in a crisis: it moved to where water remained. The Tiber, running along the western edge of the Campus Martius, was the only reliable source left. The hills emptied. People crowded into the old field, now built over and layered with centuries of rubble.

  In December 791, the Tiber flooded and the Campus Martius was entirely submerged. Flooding was a recurring threat for a district that sat between 3 and 8 meters above the river's level. Yet the area persisted, because pilgrims kept coming. The Vatican stood nearby, and a continuous stream of visitors brought wealth. The river itself supported a thriving economy.

  The Via Cassia, entering Rome through the Porta del Popolo in the northern Campus Martius, became the most important road connecting Rome to the rest of Europe; it linked the city to Viterbo, Siena, and Florence. The alternative route, the Via Aurelia along the coast, became dangerous in medieval times because of malaria spreading through coastal marshes and because Saracen pirates raided the seaside towns along its path.

  The twelfth or thirteenth century writer known as Magister Gregorius looked down from one of Rome's hills and noted that the great ancient structures had been replaced by a forest of medieval towers. In 1513 to 1521, Pope Leo X built a road from the Porta del Popolo to the Vatican, first called the Via Leonina after himself, later renamed the Via di Ripetta after the river port it ran alongside. In 1555, Pope Paul IV designated part of the southern Campus Martius as the ghetto for Rome's Jewish population.

• 7. The Modern Layer

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  Rome became the capital of the newly established Kingdom of Italy in 1870, and the Campus Martius was pulled into a new era of growth. The population that had declined after the Renaissance began rising again. Protective embankments were built along the Tiber to stop the recurring floods that had threatened the district for centuries.

  Those embankments solved one problem and created another. The tall walls cut off the ancient embarkation point called the Ripetta, which translates roughly as "little bank," along with the narrow streets that had wound down to the river and the vernacular buildings that had lined the water's edge for generations. The old relationship between the city and its river was severed by the infrastructure meant to protect it.

  Montaigne's observation from 1581, that the old streets lay more than thirty feet below the present ones, captures something essential about what the Campus Martius actually is: not a place preserved from antiquity, but a place layered over and over, each era building on the debris of the last. The IV rione of Rome, called Campo Marzio, still carries the old name, though it covers only a smaller section of the original two-square-kilometer area. Beneath the streets of that neighborhood, the foundations Montaigne described are still there.