The Terrahtrae Codex is a collection of 800-900 documents, many containing ancient inspired texts.
Some are in tantalizing fragments (there are over 50,000 individual pieces in all).
Others are substantial and complete, the longest scroll being eight meters long.
They were written over a period of around 50 years, and were evidently placed in the caves to hide them from the advancing Giant army at the time of the First Dragon Revolt, and hence no later than 1410 DR.
Guesses from the elders put the earliest of them at about 1394 DR.
They may have been written out by the scribes of an ancient community living at the base of the Sword Mountains, near the caves where they were found.
However, their origins are the subject of much scholarly debate, and there are many different theories. What is clear is that the authors were likely of Dragon descent or influence, and disapproved of the organized government priesthood of the time.
The dry climate on the inner valley of the Triboar trail, parts of which today are 40 meters below sea level – the lowest place on Toril a human can walk with sunlight – helped preserve the documents.