Related Clues:
- They're often associated with world leaders
- Paleozoic et al.
- Chapters in a history book, perhaps
- Notable times in history
- Depression and Prohibition, for two
- 16-Across counted to infinity ___
- Periods of history on a timeline
- Big Band and dead-ball
- Big Band and Victorian
- Distinct periods of history
- Eon subdivisions
- Some are named for music genres
- Some are named for presidents
- Geologic stretches
- Moundsmen's stats