From Halopedia, the Halo wiki
Only two reliquaries are known. The first was likely the planet Ulgethon, a world in Sangheili territory with Forerunner relics where the Sangheili and San'Shyuum encountered each other. The second was the human-colonized world of Harvest, which was glassed by the Covenant believing the humans had destroyed or stolen the relics present, leading to the Human-Covenant War. In reality, the signal being read by Covenant scans as Forerunner artifacts to be reclaimed were in fact individual human beings, who were all labeled as Reclaimers until scanning technology was altered to prevent that knowledge from falling to the general Covenant populace.