The panel is probably part of the predella of Lorenzetti's 'Birth of the Virgin' of 1342, painted for the altar of Saint Sabinus in Siena Cathedral (now in the Museo dell' Opera del Duomo, Siena). It was one of four altarpieces, showing the life of the Virgin, for the altars of the four patron saints of Siena.
Pietro Lorenzetti's altarpiece was flanked by figures of Saints Sabinus and Bartholomew and the National Gallery painting was presumably below the first. It apparently illustrates a rare episode showing Venustanius, the Roman Governor of Tuscany, trying to persuade Saints Sabinus, Marcellus and Exuperantius to worship a pagan statue, here apparently Venus since she is shown holding a golden ball representing the apple Paris gave to her.
