When the Kingdome was conceived in the early 1970s, the notion of a nine-acre roof made of concrete, unique in the world, seemed preposterous. It wasn't. At least, for 24 years and host to four major sports teams, it wasn't.
When in the middle 1990s the plans for a replacement baseball park were disclosed, they included a first-of-its-kind, giant steel retractable roof that ran on railroad tracks. How 1880s. How implausible. The project just passed its 20th anniversary.