The Capitoline Hill was equivalent of the ancient Greek acropolis. Several important Roman temples are built on Capitoline Hill.
Similar to most of Michelangelo’s project, the commissioner was thrilled to accept artist’s proposals which exceeded all expectations.
It is a story of shifting the center of the world. Such an ambitious project could not have happened over night. That it took 400 years to be completed, would have been a great surprise even to the artist himself.