It’s The-Covenant-Which-Must-Not-be-Named due to White Wolf owning the ongoing trademark. It’s the one in the Pyrenees named after a Tibetan temple, the same one with all the weird highly competitive Mercurians.
If you’re using older ArM3 era Provencal material (such as ArM3 Covenants, Mistridge or the Four Seasons Tetralogy), just substitute with Aedes Mercuriae (Latin: “the Altar/Temple of Mercury”) and everything pretty much works out OK to be honest.
Just don’t mention the Albigensian Crusade…
My Life as a Grog 
Remember that since Aedes Mercuriae is technically multiple sites, the one on the Pic du Midi d’Ossau is usually referred to Dorsum Templum (“the back of the temple”), which in the dialect of the region would probably sound something like a word that starts “Dois…” 🙂
“Just don’t mention the Albigensian Crusade…”
I did, but I think I got away with it! – Basil Fawlty