The was a small but important group—it was actually one of Valéry's most cherished collections of friends since everyone in it was dedicated to the alexandrine, which is known as the "leading measure in French poetry." The alexandrine has very exact numbers of syllables and pauses, and it has all sorts of other rules (if you want details, go here). The point, however, is that this group loved writing and reading poems that were not exactly free-form and flowing. A poem has to obey some serious rules if it wants to call itself an alexandrine.
Never mind that it took him four years to write this thing—the point is that Valéry wrote a monster poem in alexandrine verse. The thing was called "La Jeune Parque" ("The Young Fate"), and it clocked in at 512 lines. 512 lines of alexandrine, people. If you love to read about the nature of human existence and the problem with immortality, this is the thing you have been waiting for.
The group had to have Baudelaire in it to offset the stuffiness of a group dedicated to such a controlled poetic form. Baudelaire brought some sauciness and rebellion to the group; and there's no doubt about it—the guy could also write a mean alexandrine. Check out these racy lines from "The Jewels":
My well-beloved was stripped. Knowing my whim,
She wore her tinkling gems, but naught besides:
And showed such pride as, while her luck betides,
A sultan's favoured slave may show to him. (Source)
Not bad, eh?
Paul's surrealism really kept things lively for this group. They welcomed Paul in, even through he was sort of an outsider to their traditional scene. (He was just so experimental.) Maybe that's why he didn't always follow the rules exactly. He'd throw a variation in here and there, but the group usually turned a blind eye to it.