Rome, Capitoline Hill, Piazza del Campidoglio, view to north, marble statues of Castor and Pollux.

The existing design of the Piazza del Campidoglio and the surrounding palazzi was created by Renaissance artist and architect Michelangelo Buonarroti in 1536–1546. At the height of his fame, he was commissioned by the Farnese Pope Paul III, who wanted a symbol of the new Rome to impress Charles V, who was expected in 1538. Michelangelo's first designs for the piazza and remodelling of the surrounding palazzi date from 1536. He reversed the classical orientation of the Capitoline hill, in a symbolic gesture turning Rome’s civic center to face away from the Roman Forum and instead in the direction of Papal Rome and the Christian church in the form of St. Peter’s Basilica. Executing the design was slow: Little was actually completed in Michelangelo's lifetime (the ‘’Cordonata’’ was not in place when Emperor Charles arrived, and the imperial party had to scramble up the slope from the Forum to view the works in progress), but work continued faithfully to his designs and the Campidoglio was completed in the 17th century, except for the paving design, which was to be finished three centuries later. An interlaced twelve-pointed star makes a subtle reference to the constellations, revolving around this space called Caput mundi, Latin for "head of the world." This paving design was never executed by the popes, who may have detected a subtext of less-than-Christian import. Benito Mussolini ordered the paving completed to Michelangelo's design — in 1940.

Michelangelo devised a monumental wide-ramped stair (the cordonata), gradually ascending the hill to reach the high piazza, so that the Campidoglio resolutely turned its back on the Roman Forum that it had once commanded. It was built to be wide enough for horse riders to ascend the hill without dismounting. The railings are topped by the statues of two Egyptian lions in black basalt at their base and the marble renditions of Castor and Pollux at their top.

The Capitoline Hill (Latin: Collis Capitōlīnus; Italian: Campidoglio), between the Forum and the Campus Martius, is one of the Seven Hills of Rome. It was the citadel (equivalent of the ancient Greek acropolis) of the earliest Romans. The name capitol seems to have meant "dominant height", although ancient tradition places its origin in caput ("skull": a specific skull found while laying the Temple of Jupiter foundation). By the 16th century, Capitolinus had become Capitolino in Italian, with the alternative Campidoglio stemming from Capitolium, one of the three major spurs of the Capitolinus (the others being Arx and Tarpeius). The Capitoline contains few ancient ground-level ruins, as they are almost entirely covered up by Medieval and Renaissance palaces (now housing the Capitoline Museums) that surround a piazza, a significant urban plan designed by Michelangelo.

more on https://en.wikipedia.org/wiki/Capitoline_Hill

picture generously provided by Rudolf Kaufmann (2015)