The Lady with a Unicorn is a painting that has evolved as circumstances changed. The secrets of these changes were revealed after radiological studies, extensive cleaning & subsequent removal of over-painting. Originally painted in 1505-6, it was a portrait of a not-so-young woman holding a dog, which is believed to be a symbol of fidelity, and the painting was perhaps executed as part of a betrothal. As the accepted story goes, when the marriage did not take place, a unicorn was substituted, which symbolized purity or chastity, but is also considered to be a phallic symbol (Szakolczai). In the 17th century it was extensively painted over to become a rather poorly done portrait of St. Catherine with a different face, a more modest dress, & the unicorn was obscured by a wheel.
Szakolczai, Arpad. Sociology, Religion and Grace. N.p.: Routledge, 2007. 271-5. Web. 25 Apr. 2015