Where does Octavius meet Marcus Vipsanius Agrippa, Quintus Salvidienus Rufus, and Gaius Cilnius Maecenas?

When Gaius Octavius is seventeen-years-old, he meets his soon-to-be best friends while participating in military training in Spain: Marcus Vipsanius Agrippa, Quintus Salvidienus Rufus, and Gaius Cilnius Maecenas.