Trips to Rome Box Office, Piazza dei Cinquecento 51, outside Termini Station's main exit. The bus waits on the same square, just across Via Cavour — look for the orange open-top bus. Please be at the stop by the time shown on your booking; the bus is already waiting.
The later evening departure ends at Piazza dell'Esquilino, in front of the rear entrance of Santa Maria Maggiore, a few minutes' walk from Termini Station. The earlier departure returns to the Termini starting point.