Of course, the ancient world has something of a reputation for astonishing structures. Indeed, in the era of the Byzantine Empire, the author Philo of Byzantium wrote a work that he called De septem mundi miraculis, or On the Seven Wonders of the World. And in the treatise, Philo describes seven “themata,” or things to see. These days, we might call them must-sees. In the writer’s opinion, they were the most remarkable feats of engineering and art in the ancient world – and therefore places that every traveler should visit.