Portico d'Ottavia in Rome

You're standing at the Porticus of Octavia, in the old Sant'Angelo quarter of Rome. What you see in front of you is a gateway. It was the southern entrance to a huge complex, and it's the only part of it still standing. Look at the tall marble columns with their Corinthian capitals. They're 8.6 metres high. On top sits a beam crowned with a triangular pediment. See the brick arch between the columns? Two columns once stood there. They were replaced after an earthquake in 442.