The Migratory Era (concept)
The Migratory Era of Marcher history (not to be confused with the much later, Sjalvolki Migrations of the 13th century) refers to the period in which the proto-Chevaliens first arrived in what would become their permanent home.
Coming in from the east in the late 1st century BI — in order to escape thralldom under a now long-dead empire, if tales are to be believed — they would encounter the Gallicader, the native inhabitants of the region, with whom they'd wage brutal warfare for decades to come. Eventually, this would end in the Gallicader largely exiting the stage of major historical importance, the codification of the Lifepath system, and the founding of the first ostensible 'High Kingdom' (though its form would bear little resemblance to its contemporary counterpart). They were led by 'Good King' Bastione, who embodied what would today be considered an ideal monarch in Chevalien eyes - if in fact he had actually existed, which is a matter of some historical dispute.
From the outset, despite their victory over the former denizens of Chevalie, they would be given little respite in peace, for conflict with the Oejeynicans of the north (which they had themselves provoked, in large part), the Kathanouxaic Empire of the south, and ultimately, the Liches, would all come to be existential threats. It was the defeat of the first Arch Lich, Vilas Venslau, that would mark the end of the Migratory Era in most conventional historians' eyes.