Thousands of years of oppression?

Yeah one of the Cessair members says this...does that mean...it's an Ancient Civilization/Cult that wanted to see Macha Rise? I mean Heart was certainly waiting for it.

Well remember, a few hundred years isn't that old for a Tuatha, I would say a few generations, not ancient. But we do not know if that was Heart's intent, to summon Macha (or become Macha, unclear on what really happened).

Wouldn't that make them Partholons or something? I mean, Tuatha began when Shakespeare arrived.

There was at least one other mention of Cessair during G10 Neamhain's Memorial, it's in the cutscene seen here: http://www.youtube.com/watch?v=ZuNgqc9-Y9w
I did that quest a few days ago and the spelling is corrected to say Cessair in place of Quasar.

Holy shit, everything in that cutscene is happening in the Saga. (Except more flowers are blooming in Connous and Physis, not less.)
As for the Partholon thing, that is unclear.

Ok, I found something more. The words in that cutscene are not the first time they are heard in similiar form. Nele's song about Macha from G3 (The Goddess' Curse, full text accessible here [1], scroll down to Nele) uses a sentence "Dé Danann's warriors on the other side of Heaven" in place of "Descendants of Cessair" from the cutscene. Nearly everything is pictured exactly the same in both the cutscene and the song.
So if we put all the information together, if Tuatha De Dananns are descendants of Partholons and at the same time are descendants of Cessair... That would make Cessair the same as Partholonians.

...strange stuff indeed...

Actually, I'm interested when does the sentence that started this discussion appear during the game. Apart from that, I found something small, but I think it could be quite relevant to the topic. During G11 quest "Goddess Needle" Python Knight states the following: "For thousands of years, I've waited". The sentence in the topic also states "thousands of years". Quite a coincidence, but if we take into account Python Knight's identity and the fact that we're trying to connect Partholons and Cessair, this finding could reinforce the theory.

Mm, that does make sense, considering that Gods tried to massacre the Partholons and in return Python Knight wanted revenge. I'd be a bit surprised if he actually returns.

... I... heard something about Cessair in G7 or G8. Something about being Adniel's first conductor that was swallowed by darkness.

I never did G7 so I have no idea, and the Strategy Guide doesn't seem to mention anything about Cessair.

Going through (or...trying...) G7 and eeeeventually G8 *shrugs*

I'll keep detailed notes if needed or...even a script.

Oh, Aubog found it. Thank you.

“	Dian Cecht ruled over the Cessair. Our power came from a contract with a great golden dragon.	„
—Cessair's Heart, Iria II: Episode 6 - Ritual and Sacrifice

So, it's confirmed. Cessair / Heart were the former conductor of Adniel.