Moon-letters

Moon-letters are a special kind of rune invented by the Dwarves, written with silver pens and designed to remain invisible under ordinary light. They can only be seen when the moon shines behind them, and for the more cunning sort, the moon must be of the same shape and season as the day when they were written. This makes them a secret and conditional form of communication, known only to those who understand their nature and the precise astronomical conditions required for their revelation.

Discovery and Reading at Rivendell

The moon-letters appear on Thror's Map, the plan of the Lonely Mountain that Gandalf gives to Thorin Oakenshield. During the company's stay at Rivendell, Elrond examines the map by moonlight and discovers the hidden writing. He holds the map up to the broad silver crescent of the moon, and the white light shining through it reveals the moon-letters beside the plain runes that describe the door's dimensions. The message reads: "Stand by the grey stone when the thrush knocks, and the setting sun with the last light of Durin's Day will shine upon the key-hole." This instruction provides the crucial clue for locating and opening the secret door into the Mountain.

Significance for the Quest

The moon-letters are essential to the success of Thorin and Company's quest. Without them, the dwarves would have no way of knowing the specific conditions under which the hidden door could be opened. The message directs them to wait for Durin's Day, the first day of the dwarves' New Year, when the last moon of autumn and the sun are in the sky together. This knowledge, combined with the key that Thorin carries, ultimately allows them to open the secret entrance and gain access to the dragon's lair. The moon-letters thus represent a piece of ancient dwarven wisdom that bridges the past and the present, enabling the heirs of Thror to reclaim their heritage.