Learn Italian: Ho studiato a Roma per tre anni. - I studied in Rome for three years.

We use per because the action is completely finished. The person studied in Rome for a set amount of time in the past, but they aren't studying there anymore. If the action were still happening (like "I have been studying in Rome for three years"), you would use da and switch to the present tense: Studio a Roma da tre anni.

How does using per for time affect the verb tense in this sentence?

Because per tre anni describes a completed, closed block of time, it pairs naturally with the passato prossimo (ho studiato). It tells us exactly how long the finished action lasted from start to finish.

Why do we use a before Roma when in English we say "in Rome"?

In Italian, you always use the preposition a for cities (like a Roma, a Milano). The preposition in is saved for countries, regions, and large islands (like in Italia or in Toscana).

Could I put the time phrase at the beginning of the sentence?

Yes! You can say Per tre anni ho studiato a Roma. Moving the time phrase to the front is grammatically correct and just puts a little more emphasis on the duration of your studies rather than the location.