In 490 BC, Pheidippides ran from Athens to Sparta to seek help in the Battle of Marathon, inspiring the race that millions of runners attempt each year. This hour, we’ll talk with ultramarathoner Dean Karnazes, who traced Pheidippides’ 153-mile path using only the comforts available during the original run. He writes about the experience in “The Road to Sparta: Reliving the Ancient Battle and Epic Run that Inspired the World’s Greatest Footrace” (Rodale).