La nascita dei Musei Capitolini risale al 1471, quando papa Sisto IV donò al popolo romano un gruppo di statue bronzee, costituendo il primo nucleo della collezione conservata fino ad allora nel Laterano. In seguito, i papi arricchirono queste collezioni con opere provenienti dagli scavi di Roma, del Vaticano o acquistate appositamente per il museo, come la Collezione Albani. Alla fine del XIX secolo, le collezioni archeologiche si arricchirono notevolmente con i reperti degli scavi effettuati durante l'edificazione di intere aree della città, ormai capitale d'Italia. Le collezioni dei Musei Capitolini sono esposte all'interno dei due edifici che, insieme a Palazzo Senatorio, delimitano Piazza del Campidoglio: Palazzo dei Conservatori e Palazzo Nuovo, collegati tra loro da una galleria sotterranea che ospita la Galleria Lapidaria e conduce all'antico Tabularium, i cui monumentali portici si affacciano sul Foro Romano.

The first square to be built following Michelangelo’s criteria of a uniform design, in modern Rome, stands on Capitoline Hill (Capitolium), where a very ancient village was located and where numerous temples were dedicated to Roman gods. Piazza del Campidoglio, until then seriously neglected, was deeply modified in 1536 when Pope Paul III commissioned Michelangelo to complete the overall arrangement of the square, on the occasion of the visit to Rome of the Spanish Emperor Charles V. The Florentine architect built an elegant podium for Marcus Aurelius’ equestrian statue and placed it in the centre of the hill in 1537, creating the centrepiece of the new urban design. Michelangelo also designed an imposing wide step staircase, named the "Cordonata" in order to allow knights to climb easily, culminating in the solemn balustrade, surmounted by classical marble groups which were placed here in the following decades.

In Piazza Bocca della Verità is the ancient marble mask, one of the most famous symbols of Rome, placed in 1632 in the pronaos of the Basilica of Santa Maria in Cosmedin. The large tondo has a diameter of about 1.80 meters and was probably a sewer cover from the Roman age. It dates back to the reign of Tarquinio the Superb, the last of the seven kings of Rome who built the Cloaca Maxima, a grandiose drainage channel. The canalization system started from the Suburra, crossed a part of the current Rione Monti, the Forum, the Velabro and the Forum Boarium, and flowed into the Tiber, near Ponte Emilio (Pons Aemilius). The name "Mouth of Truth", originated in 1485, is linked to a curious and fascinating medieval legend, according to which the mouth could bite the hand of liars. The tradition was widespread among jealous husbands, who brought their wives to the monument: after introducing their hand, women had to declare that they had not committed adultery.

In Piazza Bocca della Verità, adjacent to the Temple of Portunus, stands this small and enchanting circular temple, the oldest surviving marble building in Rome. Incorrectly called the Temple of Vesta, it was dedicated to Hercules Victor, patron saint of the merchants who operated in the nearby Forum Boarium. The area, located between the Tiber, the Capitoline Hill, the Palatine Hill, and the Aventine Hill, was used as a livestock market. Also known as Hercules the Unconquered or Hercules the Olive Tree, the temple was likely built by the architect Hermodorus of Salamis towards the end of the 2nd century BC. The building, constructed of Greek marble, features twenty Corinthian columns resting on a stepped base of tuff blocks. Some columns are made of Luni marble, attributable to the restoration carried out under Tiberius, likely after the flood of 15 AD.

The complex of the Portico d'Ottavia is the only one preserved of the large porticoes that limited the square of the "Circo Flaminio" on the northern side. This area today corresponds to the ancient Ghetto. Between 27 and 23 BC, it was rebuilt by Augustus, in place of the oldest Portico of Metellus, and dedicated to his sister Ottavia. It was later restored and partially rebuilt in 203 by Septimius Severus, after a fire in 191, a period to which most of the currently visible remains belong. The complex, a four-sided portico of 119 x 132 meters, included the "Temple of Juno Regina", which was then joined by the "Temple of Jupiter Stator", the first in Rome entirely in marble, two libraries, Greek and Latin, and the Curia Octaviae, a large public meeting space. Today, only the south-eastern corner and the entrance vestibule of the complex remain.