These are the remains of a hidden gem in Roma. This was a temple dedicated to the deified Emperor Hadrian by his successor Antoninus Pius.
The pieces that remain today are what you see, eleven columns with Corinthian bases and capitals. The rest disappeared some time ago.
This set of Roman remains is located close to the Column of Aurelius. It is another one of those that if you are interested in Roman history, you should make the detour to see what’s left of this temple. There’s nothing cooler than seeing ruins from 1800 years ago.