Several important temples were built at the Capitoline Hill by the Romans: the Temple of Juno Moneta, the Temple of Virtus and the Temple of Jupiter Optimus Maximus Capitolinus, the most important temple in ancient Rome. The latter was built in 509 BC and was almost as large as the Parthenon in Athens.

Statue of Marcus AureliusAlso on the hill was the Tabularium, built in 79 BC and used as the empire's main archive.

The hill, and the temple of Jupiter in particular were the symbols of Rome as Caput Mundi, capital of the world.

During the middle ages, the site became the center of civic government and several palaces were built on the hill. But when Charles V planned a visit to Rome in 1536, the muddy Capitoline Hill was in such a bad shape that Pope Paul III Farnese asked Michelangelo to design a new square, the Piazza del Campidoglio, including a redesign of the existing 
Piazza del Campidogliobuildings surrounding the square.

Michelangelo came up with an original design for the square, including an intriguing ground pattern. He redesigned the Palazzo Senatorio, seat of the Roman senate. Michelangelo also made designs of a new façade for the Palazzo dei Conservatori and designed a new building, the, Palazzo Nuovo. 
Also in the plans were a monumental staircase, the Cordonata, leading from the bottom of the hill to the new square. Construction of the Piazza di Campidoglio started in 1546 but only the staircase at the entrance of the Palazzo Senatorio was completed when Michelangelo died in 1564.

The project was only finished in the 17th century, but most of Michelangelo's designs were implemented.