Early history

Thousands of Years ago

An early Cro-Magnon, later to take the named Vandal Savage, is given immortality by a strange meteor. (JL: Maid of Honor)
Mankind wages war with the reptilian Ophidians, and emerges victorious. The last Ophidians create the Heart of Darkness, which is sealed away in a temple and guarded by humans for millenia. (JL: Eclipsed)
A young Amazon warrior named Hippolyta has an affair with Lord Hades. After attempting to overthrow the Olympic Gods, Hades is banished to the underworld. Hippolyta and her Amazon tribe are forced to guard the gates to Tartarus for eternity. No man is allowed to set foot on their new home Themyscira, dubbed "Paradise Island." (JL: Paradise Lost)
Around this time, an Amazon Princess christened Diana, is created by Hippolyta, with possible assistance by Hades. (JLU: The Balance)
The ancient Atlanteans fight against the interdimensional Ichthultu, and Atlantis sinks below the waves. The Thanagarians also rejected Icthultu. (JL: The Terror Beyond)

Two Thanagarian law officers, Katar and Chay-Ara Hol fall into a wormhole and crash in Ancient Egypt. With their ship out of fuel and no other way to get home they opt to use their knowledge of advanced technology to improve the lives of the locals as best they can. (JLU: Shadow of the Hawk)

During the reign of King Arthur, a young man named Jason Blood attempts to betray Camelot to Morgaine Le Fey. His deception is discovered by Merlin, and he is bonded to the demon known as Etrigan.
Also, it is believed that the Shining Knight came from this period. (JLU: Patriot Act)

Early in the 10th Century, Prince Jon a Scandinavian warrior of great renown, know throughout the world as "The Viking Price" stood alone on a frozen battlefield as the sole survivor of a bloody conflict. It was then that he met a Valkyrie, taking the souls of the fallen warriors to Valhalla. Jon and the Valkyrie fell in love, though when Odin, king of the Norse Gods discovered the affair he banished Jon from Valhalla. After Jon pleas with Odin to allow him to be reunited with his love, Odin agrees to allow Jon into the Halls of Valhalla on the condition that he die a heroic death. However, out of cruelty Odin gifts Jon invulnerability from harm by metal, wood, fire and water, preventing Jon from achieving his goal. After many years travelling the world, fighting many battles, searching for his heroic death Jon eventually tires of the endless bloodshed and having grown distant from humanity sails into the frozen north, where he passed out of living memory. (JLU: To Another Shore)

The Martians fight a war against the Imperium, culminating in the destruction of the Martian civilization. Only one Martian, named J'onn J'onzz, survives. (JL: Secret Origins)

The New Gods known as Darkseid and Highfather exchange infant sons in a pact to keep peace between Apokolips and New Genesis. (TNSA: Apokolips... Now!, Part I)

An alternate version of David Clinton travels to this year from the mid-2000s and loses his technology to Tobias Manning. Batman, the Green Lantern, and an alternate version of Wonder Woman arrive to search for Clinton and run into Jonah Hex, Bat Lash, Sheriff Ohiyesa Smith, and El Diablo. Together they all take down Manning and the three Leaguers are sent to their future. (JLU: The Once and Future Thing Part One: Weird Western Tales)

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