At length the Duke desired him to paint a picture of the Last Supper on the wall of the refectory in the Convent of the Madonna delle Grazie. This was his greatest work in Milan and a wonderful masterpiece. It was commenced about 1496, and was finished in a very short time. We must now judge of it from copies and engravings, for it has been so injured as to give no satisfaction to one who sees it. Some good copies were made before it was thus ruined, and numerous engravings make it familiar to all the world. A copy in the Royal Academy, London, was made by one of Leonardo's pupils, and is the size of the original. It is said that the prior of the convent complained to the Duke of the length of time the artist was spending upon this picture; when the Duke questioned the painter he said that he was greatly troubled to find a face which pleased him for that of Judas Iscariot; he added that he was willing to allow the prior to sit for this figure and thus hasten the work; this answer pleased the Duke and silenced the prior. After a time misfortunes overtook the Duke, and Leonardo was reduced to poverty; finally Il Moro was imprisoned; and in 1500 Leonardo returned to Florence, where he was honorably received. He was not happy here, however, for he was not the one important artist. He had been absent nineteen years, and great changes had taken place; Michael Angelo and Raphael were just becoming famous, and they with other artists welcomed Leonardo, for his fame had reached them from Milan. However, he painted some fine pictures at this time; among them were the "Adoration of the Kings," now in the Uffizi Gallery, and a portrait of Ginevra Benci, also in the same gallery. This lady must have been very beautiful; Ghirlandajo introduced her portrait into two of his frescoes. But the most remarkable portrait was that known as Mona Lisa del Giocondo, which is in the Louvre, and is called by some critics the finest work of this master. The lady was the wife of Francesco del Giocondo, a lovely woman, and some suppose that she was very dear to Leonardo. He worked upon it for four years, and still thought it unfinished: the face has a deep, thoughtful expression--the eyelids are a little weary, perhaps, and through it all there is a suggestion of something not quite understood--a mystery: the hands are graceful and of perfect form, and the rocky background gives an unusual fascination to the whole picture. Leonardo must have loved the picture himself, and it is not strange that he lavished more time upon it than he gave to the great picture of the Last Supper (Fig. 37).