The fact that you need to be behind the Campidoglio to view the Forum offers one clue about the long and twisted history of Rome.
Left: the Temple of Saturn
Right: The Temple of Saturn (eight columns) and the Temple of Vespasian (three columns)
When Rome emerged from the Middle Ages and the Renaissance bloomed, life was no longer centered around the Forum, but around the river and the area near the Vatican. Michelangelo literally turned the city's attention away from its past through his architectural skills.