The 1st Rome's Colisseum. It's smaller than the famous one but is awesome like it.
Not to be mistaken for the Colosseum, this is only a very short walk from Piazza Venezia, so it should definitely be something to be seen.
it is less than 10 minutes walking
Similar to Colosseum.
The Theatre of Marcellus is an ancient open-air theatre, built in the closing years of the Roman Republic. It was named after Marcus Marcellus, Emperor Augustus's nephew, who died five years before its completion. Today the upper portion is divided into apartments, and its surroundings are used as a venue for small summer concerts.