[Aldus Manutius] Silver Denarius of the Emperor Titus, minted 80 A.D. In the Adagia of Erasmus (II.i.1), it is stated that Pietro Bembo gave Aldus Manutius this coin, from which Aldus “borrowed” the image of a dolphin and anchor, a symbol of the favorite maxim of Augustus: “Make haste slowly.”
It is believed this coin was minted as part of a series of coins to commemorate the prayers voted by the Roman Senate following the catastrophic eruption of Mount Vesuvius in 79 A.D. In that ceremony, sacred couches or pulvinaria were arranged to bear symbols of a particular deity. The dolphin and anchor represented Neptune.
See: Harold Mattingly, Coins of the Roman Empire II, London, British Museum, p. 235: 72. Anders Ollfors, “The Anchor and the Dolphin and Some Other Printers’ Devices,” in Dais Philestephanos. Studies in Honor of Prof. Staffan Fogelmark, Uppsala, 204, pp. 322-331.