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Apparently an ancient technique, but the moon-letters on Thrór's Map (our only known example) were made sometime between III 2770 and c. III 2790;1 and read in Rivendell in III 2941
Particularly associated with Dwarves
Those on Thrór's Map described a hidden Dwarf-door leading into Erebor, the Lonely Mountain
So named because moon-letter runes could only be read when the Moon shone behind them


About this entry:

  • Updated 21 November 2020
  • This entry is complete


The secret runes of the Dwarves

" 'Moon-letters are rune-letters, but you cannot see them,' said Elrond, 'not when you look straight at them.' "
The Hobbit 3
A Short Rest

A system of writing invented by Dwarves, moon-letters were ordinary runes, but written in such a way that they could only be read when the light of the moon shone behind the writing. Some moon-letters could be read by any moonlight, but it was possible to make the writing even more secret. More sophisticated moon-letters could only be read by the same shape of moon, or at the same time of year, as when they were written.

Moon-letters were written with silver pens. The substance ithildin, made from mithril, reflected only starlight and moonlight, and it seems likely that ithildin, or something very similar, was used by the Dwarves to write their moon-letters.



In Rivendell, Elrond observed that the moon-letters on Thrór's Map must have been under the same crescent Moon at Midsummer that was then in the sky. The Moon's phase recurs like this on a cycle of almost exactly nineteen years, so we can calculate back to find the likeliest date the Map was made, a calculation that gives us two possible dates. These particular moon-letters must have been inscribed either in III 2770 (that is, the same year that Smaug drove the Dwarves from Erebor) or nineteen years later in III 2789 (just before Thrór gave the Map to his son Thráin). Either date would fit the established timeline, but if Elrond is right about the crescent Moon, one of these two dates must be the correct one.

See also...

Thrór’s Map


About this entry:

  • Updated 21 November 2020
  • This entry is complete

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