What Once Was Believed is an insert set in 2015 Topps Allen and Ginter. Each card carries a WAS prefix.
Gallery[]
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Checklist[]
| Number | Belief |
| 1 | Flat Earth |
| 2 | Open Polar Sea |
| 3 | Ether |
| 4 | Four Classical Elements |
| 5 | Alchemy |
| 6 | Brontosurus |
| 7 | Rain Follows the Plow |
| 8 | Phrenology |
| 9 | California Island |
| 10 | Geocentric Solar System |
Template:2015 Topps Allen and Ginter