Rome's most sprawling hill—the Esquiline—lies at the edge of the tourist maps, another Rome. Even Imperial Rome could not have matched this minicosmopolis for sheer internationalism. Right around Termini, sons of the soil, the so-called "romani romani," mingle with Chinese, Sri Lankans, Sikhs, and a hundred nationalities in-between. But not all of this area has the same gritty, graffiti-filled atmosphere you find near the station. Closer to the Colosseum, the Celian Hill area, called “Celio” by locals, is a tranquil, lovely residential area replete with medieval churches and ruins. On the other hand, Monti, a quarter stretching from the Forum to the Basilica of Santa Maria Maggiore, is a rione (district) dating back to ancient times, when gladiators, prostitutes, and even Caesar made their homes here. Today, Monti is one of the best-loved neighborhoods in Rome, known for its appealing mix of medieval streets, old-school trattorias, and hip boutiques.

The Esqueline and Celian hills take in some of the city's best sights, including Michelangelo's Moses, the Baths of Caracalla, and dazzling Early Christian mosaics at San Clemente and San Pudenziana. Historically speaking, it also took in some of the worst, including the Suburra, Rome's most notorious slum—today, Monti. A dark, warrenlike sector of multistory dwellings populated in part by gladiators from the nearby Colosseum, it lived by its own rules, or lack of them. The empress Messalina would often venture here for illicit pleasures. So mean were the Suburra's streets that it's thought that the great fire of AD 64, which all but destroyed the neighborhood, may have been ordered by Nero as a public-order measure. But elsewhere on the Esquilino and Celio, Augustus built impressive public markets and the area became the "in" place to be. Palaces of ancient Rome's who's who sprang up with sumptuous gardens to match.

Signs of this remote past are everywhere. The Colosseum's marble-clad walls loom at the end of narrow, shadowy streets with Latin-sounding names: Panisperna, Baccina, Fagutale. Other walls, built for the Caesars, shore up medieval towers. Amid the hints of antiquity, several great churches of the Christian era stand out like islands, connected by broad avenues. The newer streets—laid out by the popes and, later, by city planners at the time of Italy's unification—slice through the meandering byways, providing more direct and navigable routes for pilgrims heading to majestic Santa Maria Maggiore, its interior gleaming with gold from the New World, and San Giovanni in Laterano, with its grand, echoing vastness.

Via Cavour, the area’s main drag, extends through the old Suburra to the rough and ready quarter around Termini, Rome's central train station. Predictably gritty, although not unsafe, this area is undergoing a steady transformation as immigration diversifies the face of the city. North of the station, Ethiopian and Eritrean restaurants abound, while just south of the station, Piazza Vittorio and its surrounding streets are an ethnic kaleidoscope, full of Asian and Middle Eastern shops and restaurants. A highlight is the Nuovo Mercato Esquilino, a covered market hall where goods from the four corners of the earth are sold in a multitude of languages. A walk south on Via Merulana leads to San Giovanni, a working-class neighborhood, of late colonized by trendy students, which surrounds Rome's cathedral, San Giovanni in Laterano.

Farther south lies a lovely contrast to the bustle of the Esquiline and San Giovanni quarters: the quiet and green Celio (Celian Hill). Like the Aventino, the Celio seems aloof from the bustle of central Rome. On the slopes of the hill, paths and narrow streets wind through a public park and past walled gardens and some of Rome's earliest churches, such as San Clemente and Santi Quattro Coronati, whose medieval poetry is almost palpable.

Far south of the Celio lies catacomb country—the haunts of the fabled underground graves of Rome's earliest Christians, arrayed to either side of the Queen of Roads, the Appian Way. The gateway to this timeless realm is one of the largest relics of ancient Rome, the Baths of Caracalla. Farther on, the church of Domine Quo Vadis announces you are entering sacred turf, as this is the spot where Jesus is said to have appeared to Peter, causing Peter to ask, Domine quo vadis? (“Lord, where are you going?”). As you venture to the catacombs, the countryside is dotted with landmarks like the Tomb of Cecilia Metella that make you feel that the days of the Caesars were not that long ago. Look down from your bus window and you will see chariot ruts.