The different interpretations of side A:

Dionysos greeting Ariadne with her sacred serpent, in the sacred grove for their marriage, symbolized by the winged cherub with a nuptial torch, in the presence of his foster-father, Silenus The story of the Emperor Augustus' supposed siring by the god Apollo in the form of a snake Peleus and Thetis, maritime deities The younger man is Mark Antony being lured by the wiles of the reclining woman (who is Cleopatra, with the snake being an asp) into losing his manly romanitas and becoming decadent, with the bearded elder male figure being his mythical ancestor Anton looking on.

The scenes on the Portland Vase have been interpreted many times with a historical or a mythological slant. It is enough to say that the subject is clearly one of love and marriage with a mythological theme. The ketos (sea-snake) places it in a marine setting. It may have been made as a wedding gift.

It is not known exactly where and when the vase was found. It is recorded as being seen in 1601 when it was in the collection of Cardinal del Monte in Italy. After the cardinal's death it was bought by the Barberini family where it remained for 150 years. Eventually, in 1778, it was purchased by Sir William Hamilton, British Ambassador at the Court of Naples. He brought it to England and sold it to Margaret, dowager Duchess of Portland, less than two years later, in 1784. In 1786 it came into the hands of her son, the third Duke of Portland, and it was he who lent it to Josiah Wedgwood, who made it famous through various copies. It was deposited in The British Museum by the fourth Duke of Portland in 1810 where it remained, apart from three years (1929-32) when it was put up for sale at Christie's, but failed to reach its reserve. It was purchased by the Museum from the seventh duke of Portland in 1945.

The bottom of the vase was probably broken in antiquity. It is likely that it originally ended in a point like a fine cameo-glass vessel from Pompeii. A cameo-glass disc, showing a pensive Priam, was attached to the bottom from at least 1826, but it clearly does not belong to the vase, and has been displayed separately since 1845.

Cameo-glass vessels were probably all made within about two generations as experiments when the blowing technique (discovered in about 50 BC) was still in its infancy. Recent research has shown that the Portland vase, like the majority of cameo-glass vessels, was made by the dip-overlay method, whereby an elongated bubble of glass was partially dipped into a crucible (fire-resistant container) of white glass, before the two were blown together. After cooling the white layer was cut away to form the design. The cutting was probably performed by a skilled gem-cutter.