Influential treasures from earlier times will be arrayed in “Heroes: Mortals and Myths in Ancient Greece,” opening at Baltimore’s Walters Art Museum on Oct. 11. This show promises to be the only blockbuster of the season, with more than 100 classical statues, reliefs, vases, jewelry and other artifacts. It combines loans from leading American and European museums but also draws from the Walters’ own collection, like so many of the exhibits opening this fall.