Ostia Antica
The books take place in the ancient time period Roman Empire during the reign of the Emperor Titus. They detail the adventures of four children who solve mysteries and have adventures in Ostia Antica, Rome, Greece, and beyond: Flavia, a rich Roman girl who lives in Ostia; Nubia, a freed slave girl from Africa; Jonathan, a rich Jewish boy; and Lupus, an orphaned mute beggar boy.