I'm thinking of axing the "stupa" as a standard special structure and just making the Great Stupa of Sanchi the Mauryan "Wonder." The Edict Pillar of Ashoka will remain a "special structure" buildable by the Ashoka hero unit. Eggbird has made an excellent high-poly Pillar of Ashoka, so we should just expand upon that (add a cool base, then a chakra on the top) for the game version, probably with a high-def normal map.