This is an ivory gravoir made in about 1320-1330 in Paris, France. It depicts Campaspe, Alexander's mistress, seated on the back of Aristotle.

The gravoir, also described as a broche or discernibulum in medieval documents, was used to part the hair and in some cases was worn as a large hairpin.

In the period between 1300 and 1325 workshops in Paris enjoyed a thriving market for secular ivory carvings. They produced mirror-cases, combs and gravoirs (hair parters), often selling them as sets in leather dressing cases. Subjects from romance literature appeared frequently, as did the allegorical Siege of the Castle of Love.
Ivory combs, together with mirror cases and gravoirs for parting the hair, formed an essential part of the trousse de toilette or étui (dressing case) of the typical wealthy lady or gentleman in the Gothic period. Considering the original ubiquity of such combs and in comparison with ivory mirror cases, a surprisingly small number survive from the fourteenth century.

The story of Aristotle and Campaspe (also called Phyllis) became widely known from the thirteenth century. It was recounted that the learned Aristotle had admonished his pupil Alexander, telling him not to be distracted from his work by the beautiful Campaspe. On setting eyes on her, however, the aged Aristotle himself immediately became so enamoured that he followed her every wish and allowed himself to be ridden by her like a horse. Campaspe, in league with Alexander, made sure that Aristotle was seen in this position by the younger man, both humiliating him and demonstrating the triumph of love over reason.