The Tablet of Ancient Wisdom is an ancient Egyptian relic said to contain the wisdom of the ancients. It describes the "Forbidden Geometry", as well as the "great Trek" into the 4th World, where one may attain godhood and immortality. The Order describes it as the "holiest of all relics".
In the early 1900s, Heinrich Kaufmann II went on an expedition to Egypt in search of the tablet, which was said to lie within the tomb of a nameless Pharoah. After one year of searching, during what The Order calls the "4th Solstice", Kaufmann located the tablet in a tomb beneath images depicting the Slender Man and what The Order refers to as the "great Trek". According to Kaufmann's journal, the locals began chanting "Gorr'Rylaehotep" in response to his discovery. His translator informed him that Gorr'Rylaehotep was the name of an ancient god that was said to have come from another world and cursed the tablet.
Kaufmann then began translating the ancient encryptions found on the tablet into a common language (presumably either English or German). The result of his efforts was a transcript that detailed the Rite of Gorr'Rylaehotep. Once translated, the tablet was considered mere fantasy by Kaufmann's colleagues and Kaufmann himself was accused of having forged his discovery. Despite this, the tablet was still moved to a British museum. The tablet, along with its transcript, were stolen from the museum in the 1930s, around the time that the Amsel and Rainwood families left the organization known as the Novus Ordo Europa (New Order of Europe) and The Order was first founded by a man who would come to be known as the First Overseer.
Now in the possession of the First Overseer, the tablet was guarded in a secret location and the information contained in the transcript was compiled into The Order's first Collective Knowledge. Eventually, the tablet and transcript were taken from The Order by the Nazis. After the end of World War II, the information the tablet contained was used by Hans Freuhauf in the Princeton Experiment, alluding to the fact that the tablet may now be in the possession of the United States government.