Where do Marseille interpretations come from?

Exactly what the title says...

As I continue to delve into the roots of Golden Dawn decks, you can see the reasoning behind why they decided, for example, that the 9 of Pentacles/Disks is about harvest and achievement. Whether you use their interpretation or form your own, at least you can understand how it came about.

But the Marseille completely confuses me since I haven't studied it yet. Where do the general conclusions about each card come from? Who decided them and how?

Thanks!