Painting is an ancient medium, dating as far back as 40,000 years ago, when early humans applied ochre and charcoal to cave walls to create images of animals or stencils of their own handprints. It was, in other words, present at the birth of symbolic thought, predating the written word by 35,000 years or so. Even with the onset of the modern era, and the introduction of photography, film and digital technology, painting has remained a persistent mode of expression, in spite of cyclic pronouncements of its death. It's impossible to say just many paintings have been limned over dozens of millennia, only that a relatively small percentage of them could be construed as timeless classics that have become familiar to the public—and not coincidentally produced by some of the most famous artists of all time. That may be stating the obvious, but it leaves open the question of what mix of talent, genius and circumstance leads to the creation of a masterpiece. Perhaps the simplest answer is that you know one when you see one, whether it's at one of NYC's many museums (The Metropolitan Museum, the Guggenheim, MoMA and elsewhere) or at institutions in other parts of the world. We, of course, have our opinion of what makes the grade and we present them here in our list of the best paintings of all time.