sentences:  The Greek historian Polybius believed that when no cause can be discovered to events such as floods, droughts, frosts, or even in politics, then the cause of these events may be fairly attributed to Tyche.Increasingly during the Hellenistic period, cities venerated their own Tychai, specific iconic versions of the original Tyche.This practice was continued in the iconography of Roman art, even into the Christian period, often as sets of the greatest cities of the empire.