The plaque depicts a subject from the Trojan War: the theft of the Palladium of Troy by Diomedes with the help of Odysseus. The composition is derived from a first-century AD Roman cornelian intaglio, formerly in the Arundel Collection and at the time part of the Marlborough Gems. The print source used by de Gault was most probably the engraving by Francesco Bartolozzi after a drawing by Giovanni Battista Cipriani, first published in 1785. The engraving, taken from an impression of the intaglio, includes the walls of Troy, a detail that de Gault edited from his rendering.

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