In 1536, when Michelangelo Buonarroti was commissioned by Pope Paul III to design an imposing square on the Capitol for the visit of Emperor Charles V, he had to include in his plans the Senatorial Palace built in the 12th century on the foundations of the Tabularium, and the mid 14th century guildhall on the south side. After their construction the main view from the Capitol was no longer of the Forum, as it had been in antiquity, but of the city opposite.
Michelangelo's design made the equestrian monument of the Emperor Marcus Aurelius, transferred to the Capitol in 1538, the dominating feature at the center of the square. He designed a stepped oval ring for the trapezoid area created by the existing buildings, placing a star-shaped ornament inside the oval with the plint of the statue at its center.
Modifications were made to the existing architecture: Michelangelo planned to renovate the facades of the two palaces already present, and to build a third, the Palazzo Nuovo, as a counterpart to the Palazzo dei Conservatori.
At the sides of these two buildings do not directly adjoin the long facade of the Palazzo Senatorio, but have space between them, Michelangelo created an open square looking west to St. Peter's, the Christian counterpart of the Capitol.
Access to the square is by way of a broad ramp, the Cordonata. Its balustrades are adorned with ancient sculptures, including the massive statues of the Dioscuri (the mythical Castor and Pollux). Construction of the piazza progressed only very slowly and in in the end it was left to other, later architects to execute Michelangelo's concept. The piazza was not finally completed until the 17th century.
Inside the Palazzo dei Conservatori and Palazzo Nuovo is exhibited the fine collection of the “Musei Capitolini”, that includes masterpiece sculptures, carvings and paints from the classic age to the Baroque.