Speculation about the identity of the woman who sat for Leonardo's iconic portrait has been rife since the turn of the 16th century, soon after it was painted. No one really knows who the dark-eyed, dark-haired beauty was, or what was behind that famous smile, though the "experts" would like you to take their theories as fact.

Most believe the sitter was Lisa Gheradini, wife of a wealthy Florentine merchant, Francesco del Giocondo. For many years the painting was known as "La Giocondo," and a discovery several years ago by a team of Canadian scientists that the lady was wearing a thin transparent gauze veil commonly worn by women who were pregnant (or about to give birth) and coincided with the date 1503 - when Lisa Gheradini was pregnant with her second child - convinced them that the merchants wife was, indeed, the sitter.

More recently, German experts at Heidelberg University Library uncovered notes in the margin of a book owned by a friend of Leonardo's mentioning that an (unnamed) artist friend of his was working on three painting - one of them a portrait of Lisa del Giocondo. This convinced them that Leonardo was the painter, the painting was the Mona Lisa, and the sitter the merchant's wife. Ultimately, it proves nothing.

Other theories range from the Mona Lisa being Leonardo's self-portrait "in drag" (the features from the two line up perfectly), to a painting of one of his lovers, to a mistress of one of his Medici patrons. Finally, there are some who postulate that the woman is da Vinci's mother, Caterina.

Half Mona Lisa, half Leonardo

The Mona Lisa

Perhaps the best argument for the latter theory is a purely emotional one. It is the only portrait that Leonardo kept with him for close to twenty years, carrying it with him when he left Italy to live out his final days in the French Court of Francois I. And it was only one of three of his paintings that he still owned when he died. That is why the Mona Lisa is now hung not in an Italian museum, but in Paris at the Lourve.

If Leonardo had painted a portrait of Giacondo's wife, why would the man have not paid for and taken possession of such a fabulous work of art? What sentimental value could that smiling lady have had for da Vinci to keep her near him till the end of his life? I choose to think Caterina is that woman. Read Signora da Vinci and find out how and under what circumstances she came to sit for the world's most famous painting .