St. Catherine of Alexandria, virgin martyr of the fourth century, was unsuccessfully tortured on a wheel which was broken by a heavenly thunderbolt and, like many martyrs, was subsequently beheaded with a sword. In this picture painted for Cardinal del Monte and, after 1628, belonging to the Barberini family, Caravaggio depicted this popular female saint, surrounded by her attributes, in a forthright and uncompromising manner which doubtless reflects her commitment to Christ but also suggests more than a little of the worldliness of Portrait of a courtesan. This was perhaps due to Caravaggio's procedure of working directly from the model in the studio and, while obviously spending a considerable amount of effort in posing the figure, rendering the detail with surprisingly few modifications.
Indeed it has been suggested that not only did he use the same model for this picture as for Martha and Mary Magdalene, but that the third finger of her left hand, hanging down limply here and propped up in an unusual way in The Conversion, was a natural deformity which Caravaggio chose not to alter. If that were the case it would help us in defining his aesthetic attitude at this time more precisely. But it seems equally possible that he merely arranged the finger in an elegant and somewhat artificial mariner for visual effect.