works were analyzed. El Greco's painting, which Picasso studied repeatedly in Zuloaga's house, inspired not only the size, format, and composition of Les Demoiselles d'Avignon, but also its apocalyptic power. Later, speaking of the work to Dor de la Souchère in Antibes, Picasso said: "In any case, only the execution counts. From this point of view, it is correct to say that Cubism has a Spanish origin and that I invented Cubism. We must look for the Spanish influence in Cézanne. Things themselves necessitate it, the influence of El Greco, a Venetian painter, on him. But his structure is Cubist." The relationship of the painting to other group portraits in the Western tradition, such as Diana and Callisto by Titian (1488–1576), and the same subject by Rubens (1577–1640), in the Prado, has also been discussed. Cézanne and Cubism Both Paul Gauguin (1848–1903) and Paul Cézanne (1839–1906) were accorded major posthumous retrospective exhibitions at the Salon d'Automne in Paris between 1903 and 1907, and both were important influences on Picasso and instrumental to his creation of Les Demoiselles. According to the English art historian, collector and author of The Cubist Epoch, Douglas Cooper, both of those artists were particularly influential to the formation of Cubism and especially important to the paintings of Picasso during 1906 and 1907. Cooper goes on to say however Les Demoiselles is often erroneously referred to as the first Cubist painting. He explains, The Demoiselles is generally referred to as the first Cubist picture. This is an exaggeration, for although it was a major first step towards Cubism it is not yet Cubist. The disruptive, expressionist element in it is even contrary to the spirit of Cubism, which looked at the world in a detached, realistic spirit. Nevertheless, the Demoiselles is the logical picture to take as the starting point for Cubism, because it marks the birth of a new pictorial idiom, because in it Picasso violently overturned established conventions and because all that followed grew out of it. Although not well known to the general public prior to 1906, Cézanne's reputation was highly regarded in avant-garde circles, as evidenced by Ambroise Vollard's interest in showing and collecting his work, and by Leo Stein's interest. Picasso was familiar with much of Cézanne's work that he saw at Vollard's gallery and at the Stein's. After Cézanne died in 1906, his paintings were exhibited in Paris in a large