Cubism remains perhaps the single most important development in the history of twentieth-century art. It was the creation of just two artists - Georges Braque, a Frenchman, and Pablo Picasso, a Spaniard - between the years 1907 and 1914. Working alongside each other in Paris, then the artistic capital of the world, they invented a way of making pictures and sculptures that broke with conventions established 500 years earlier in the Renaissance. Their...