When an observer on land watches a receding ship, the hull is the first part to sink below the horizon, and the masthead is last (conversely, when a ship is approaching, the masthead is first to rise over the horizon). The fact was familiar to Roman poets. Ovid insists on it at length in the Metamorphoses (xi. 466–71), in the story of Alcyone and Ceÿx. Valerius Flaccus puts it very neatly in the Argonautica (i. 494–7), where the women gaze at the departing sails till the sea overtops the mast, donec iam celsior arbore pontus immensusque ratem spectantibus abstulit aer.