E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Agnes (St.)
is represented by Domenichino as kneeling on a pile of fagots, the fire extinguished, and the executioner about to slay her with the sword. The introduction of a lamb (agnus) is a modern innovation, and play on the name. St. Agnes is the patron of young virgins.
1
St. Agnes was first tied to a stake, but the fire of the stakes went out; whereupon Aspasius, set to watch the martyrdom, drew his sword, and cut off her head.