Bettany Hughes Treasures of the World episode 5: The historian visits a dig in Istanbul containing artefacts from multiple eras, and follows in the footsteps of one of her heroes, Byzantine empress Theodora. She visits the restoration of the 6th-century Basilica Cistern, a marble-columned water reservoir under the city's streets, Topkapi Palace, and Europe's largest wooden building, Prinkipo Orphanage, which was once home to more than…