It’s scene out of the play ‘Orlando Furioso,’ written by Italian playwright Ludovico Ariosto in 1516. Roger is out riding the coast at Brittany on his hippogriff, a hybrid animal that is half-horse half-eagle. He spots Angelica, nude and tied to rock on the coast, left there by barbarians to be killed by a sea monster. Roger rushes over just as the monster surfaces near Angelica, and he saves her just in the nick of time.
When this painting was first exhibited at the Paris Salon in 1819, Ingres was greatly criticized for painting Angelica with a goiter, which is an abnormal enlargement of the thyroid gland in the neck. It is a weird neck when you take a good look at it.