“The circle, according to the accepted meaning, signifies eternity, because it has no end. The anchor, because it delays, slows down and stops the ship, means slowness; the dolphin represents speed, because there is no creature swifter or more agile in its onrush. So by putting these meanings together you have the phrase Always hasten slowly.”
From the 1508 Edition of Erasmus’ Adages, quoted in Phillips, Margaret Mann, Erasmus on His Times – a Shortened Version of “the Adages of Erasmus” (Cambridge University press 1967) at page 6. Erasmus wrote that festina lente, make haste slowly, was "the favorite maxim of Octavius Caesar, the chosen symbol of Titus Vespasianus in old days, and of Aldus today."
Aldus Manutius, whose name appears on the second image, was a famous Italian printer of the Renaissance, and the image was his logo. The care with which he printed books made him a favorite of Erasmus. Erasmus includes several paragraphs of praise for Aldus in his essay on festina lente.