File:CatherineBeheadCitolanzo.jpg

Girolamo Siciolante da Sermoneta The Martyrdom of St. Catherine of Alexandria Oil on panel 259 x 153 cm c. 1566–68 Altarpiece in the Cesi chapel, Basilica of Santa Maria Maggiore, Rome

Unusually, the artist has portrayed the Trinity witnessing St. Catherine's martyrdom.

Some details gleaned from:
 * Steven F. Ostrow, "The Counter Reformation and the End of the Century", in Rome, ed. by Marcia B. Hall (Cambridge: Cambridge University Press, 2005), p. 254. Google preview)
 * Fondazione Federico Zeri : Catalogo : Siciolante Girolamo da Sermoneta, Decapitazione di santa Caterina d'Alessandria