Wearing his characteristic winged hat, and with a pan flute next to his left hand, Mercury stealthily approaches a shepherd he has lulled to sleep with the unlimited powers of his music. The latter is the one-hundred-eyed Argos, whom Juno appointed to watch over Io, the beautiful nymph she had turned into a cow in order to protect her from the amorous advances of he husband, Jupiter. Fully aware of her strategy, the latter sent Mercury to bypass Argos and steal her.

This episode from Ovid´s Metamorphoses was the subject of one four mythological scenes that Velázquez painted for the decoration of the Hall of Mirrors and Madrid´s Alcázar Palace. From the standpoint of protocol and representativeness, that hall was the most important of the entire palace and its impressive panoply of paintings was part of its function. Most were either portraits of Spain´s Habsburg monarchs, or mythological or biblical scenes. The other three paintings from Velázquez´s series show Apollo flaying a satyr -a work of the same dimensions, as both were intended to hang between windows- and two somewhat smaller works depicting Venus and Adonis and Psyche and Cupid, respectively. They were all lost when the Alcázar burned in 1734. The series probably dates from the late 1650s, when the Hall of Mirrors was subjected to an intense process of decorative enrichment to make it the most sumptuous possible setting for receiving the Duke of Gramont, King Louis XIV´s ambassador, who arrived to negotiate the wedding between that monarch and Philip IV´s eldest daughter, María Teresa. This was also the context for other activities by Velázquez, including the project for decorating the ceiling with the story of Pandora, which was carried out by Colonna and Mitelli.

There has been considerable speculation about the meaning of this series, and the hall´s function has even prompted some political interpretations. The paintings were joined by their mythological nature, and the larger two share an allusion to music, while the smaller pair both allude to love. The erotic subject matter was appropriate for the ceremony that was to take place in 1659, and in fact, the story of Pandora has also received a matrimonial interpretation (Aterido and Pereda 2004). Stylistically, the only surviving canvas of the four is coherent with the artist´s works from the end of his career, when he carried his tendency to dissolve forms to its maximum consequences, blurring the limits between bodies and once again demonstrating his astonishing capacity to suggest life, movement and emotions with a few extraordinarily long and accurate brushstrokes. But Velázquez did not invent this painting ex-nihilo. As has frequently been pointed out, he based it on the Roman sculptural group that represents a dying Gaul. Like The Spinners, this work had pieces added to it: a strip approximately 25 cm. in width that runs along the entire top, and another narrower one (about 10 cm wide) at the bottom.

Fábulas de Velázquez. Mitología e Historia Sagrada en el Siglo de Oro / edición a cargo de Javier Portús Pérez, Madrid, Museo Nacional del Prado, 2007, p.336