Incunabula Obscura

A collection of lists of portents, often referred to as the "Book of Prophecies". Though the exact form may vary, most of the lists stipulate that a world-shaking event will happen if and when a number of conditions - portents - are met. Though about 20 of the events predicted in the collection have come true, critics have correctly pointed out that many of the lists have been compiled after the fact. For various reasons, some of these lists have been neglected, while others have attracted much attention. Most recently the events of the Ring Saga brought the portents into focus, especially in hindsight. Because of this, the corresponding list that is associated with the Horned One has been taken very seriously, though the attention has waned somewhat recently. 
The Incunabula Obscura is kept in Mnemthosis and is maintained by the Thoth priesthood.