Capitoline Hill.

The Capitoline Hill is free.

The capitoline hill is free, except for the interior of buildings on it. The Capitoline museum, for example, is wonderful but does charge entry. But you can walk up the hill, go around the back of the buildings and have excellent views over the forum for free. The square in front of the museum and the steps leading to it are beautiful and free as well.

A recent thread with a (sort of) similar question:

https://community.ricksteves.com/travel-forum/italy/campidoglio-view-of-roman-forum

FYI - The buildings and piazza were designed by Michelangelo - It is one of the most historically significant urban spaces from the Renaissance.

Thank you for answering my question, much appreciated

The museum is very good too and houses the original equestrian statue of Marcus Aurelius.