The Enlightenment was an event where the Gods appeared in the world, through a massive portal that lead to The Void. The details of their manifestation is unclear, nor recorded, although some historians believe it was the work of demons. It is called 'the enlightenment' because it became the starting point of civilization; mortals, up to that point, were little more than nomads and savages, lacking any real intelligence or art, which the Gods taught to them.
Science, medicine, technology, the art of war, agriculture; all facets of society were taught, slowly, leading to a rapid development of villages, which would become kingdoms or empires. Mortals worshiped the gods for their gifts, and some, in turn, were given aspects of the God, essentially siring a new race.
Still, after a point, mortals were made to fend for themselves. Heaven's Contention, a war between the divine, would lead to the death of many Gods, as well as drive many others into hiding, and this did not change at its conclusion. Mortals have been left to their own devices for centuries, causing details and beliefs to fade from most.