History in Five Songs 266: Is Black Sabbath progressive metal?

In Episode 266, Martin wonders aloud if any of Black Sabbath's catalog constitutes progressive metal.

1. Black Sabbath – “Under the Sun”
2. Black Sabbath – “Spiral Architect”
3. Black Sabbath – “Megalomania”
4. Black Sabbath – “Into the Void”
5. Black Sabbath – “Supertzar”

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