The Age of the Paladins
The Age of the Paladins is the earliest recorded history of the Realm. It was a time plagued with constant chaos, strife, war, and conflict. It wouldn't be until the actions of the Warders and original Paladins that the Realm could start moving towards an age of peace.
This information comes from this stream.
It is thought that the moon was shattered during this time period, based on a comment by Valera in The Fight of the Shattered Desert story, this dev statement revealing the moon to have shattered long long ago, and this teaser revealing the moon to have shattered centuries ago.