The beginning of the Elder Days era is unknown.
Until more material is revealed, it will be considered that the Elder Days spanned from the beginning of the Age of Men in Lemuria (circa 500,000 BC).
As Men rose to supremacy in Lemuria, "elder spirits", invisible, shapeless shapes, that crossed the dark voids of space to come to Earth in its prime began to fled from sight, awaiting to rise and rule again Earth. While other lied dormant in the ocean or beneath hills.
An eldritch god worshiped long before the Pre-Cataclysmic Age, Jhoatun Lau was said to live in a palace on an icy world far from Earth. He could only be summoned when Earth was in cosmic alignment with a planet beyond the orbit of Pluto, which only occurred "once a millennium".
The last conjunction happened 113,000 years ago. At that time, a cult worshipping Jhoatun Lau attempted to summon him by filling a massive stone bowl with the blood of warriors, in the hopes that he would take them with him when he returned to his palace among the stars. However, the eldritch god seemingly found his worshippers' sacrifice inadequate and devoured them all before somehow returning back to his domain.
The Elder Race, a seemingly humanoid race that predated humanity, composed of numerous wizards, and speculated to be descended from Elderspawn (the offspring of the Elder Gods of Earth), ruled the world in the days before the rise of the Thurian culture, which founded the Seven Empires.
Serpent-Men and Man-Serpents, Tsathoggua
The Serpent-Men worshiped Tsathoggua, an ally of Set who had come to Earth prior the rise of man. In the temple where he lived, on the Nameless Isle, the Serpent-Men hid a defective Cobra Crown under a shrine to Tsathoggua, guarded by a living stone idol of Tsathoggua,
Eventually, a Pictish shaman discovered on cave paintings or carvings that reptilians, including the Serpent-Men and the Man-Serpents, could not say nor stand to hear a certain phrase: "Ka nama kaa lajerama". Using it, the humans overthrew the Serpent-Men masters and slaughtered the Man-Serpents. After centuries of fighting, the humans erroneously believed to have annihilated both of the serpent races.
From that time of those wars with the Serpent-Men, those words became engraved in the souls of all men, and its knowledge was passed down among the Picts.
As Men rose to supremacy in Thuria, the "elder spirits" kept on fleeing, hiding from sight, awaiting their eventual triumphant return. At some point, the Sleeper went under the desert, where a temple was erected and a flame kept always burning there, and was regularly 
- The Elder Days were created by Robert E. Howard in "The Black City", an unfinished manuscript, though that name was invented by Lin Carter, who completed Howard's version as "Black Abyss" (adapted in Savage Sword of Conan #2).
- The exact scope of this era is unknown, as no clue has been given so far on its beginning. For clarity and relevancy purposes, and unless stated otherwise, this page will focus on the events occurring from 500,000 BC (the creation of the First Men, the Thousand Year War, the end of the Age of Dragons and the beginning of the Age of Man, preceding Thongor's era) to 100,000 BC (the end of the Elder Days and the beginning of the Pre-Cataclysmic Age. Thongor and his era are also creations of Lin Carter.
- Bal-Sagoth was allegedly the oldest land in the world, predating at least Atlantis, and could be set in the Elder Days, though the the exact truth behind that statement remains unknown.