Vestiges of an ancient Greek art form, preserved by catastrophe 

Fewer than 200 bronze sculptures from the Hellenistic era -- a period that began more than 2,000 years ago -- survive today. About a quarter of those are gathered in an exhibit at the National Gallery of Art called "Power and Pathos," which offers a view into the spread of ancient Greek culture around the world, and the rise of a new art form. Jeffrey Brown reports.