Christie's Chairman Marc Porter talks about Paul Allen as a collector and the role philanthropy now plays in the sale of the major art collections of our time. Max Carter discusses the challenge of estimating a wide array of artists in a collection that ranges over hundreds of years. Led by works from Cézanne, Seurat, Gauguin, Klimt, van Gogh, Boticelli, Manet, Jasper Johns, Lucian Freud, David Hockney and many more artists.