Runes was a system of writing based on angular shapes that could easily be carved into wood or stone. Originated and used mainly by northern tribes of Europe such as Anglo-Saxon and the Norse. One theory says that Runes evolved from Etruscan writing, however other quasi-runic scripts in other parts of the world (Rovasziras and Orkhon Script) exist.
In The Hobbit, Tolkien used Old English runes to display the writing of the Dwarves on the Thrór's Map; his Dwarves however were based mainly on Norse culture and their language is influenced of Semitic languages. The texts of course are modern English, and display the use of Westron of Third Age.
The 50th anniversary edition of The Hobbit includes a foreword which explains the usage of the Old English runes and help the reader read the Map (although the messages are revealed in the end of Chapter 3, A Short Rest)
Eventually Tolkien elaborated on a totally original runic writing system while writing The Lord of the Rings. Although most of the letters between historical runes and Tolkien's "cirth" are identical, they don't share the same values, since the Cirth follow the phonetic principles of the Tengwar.
In the history of Arda, a runic script called Cirth was invented by Daeron of Doriath to represent Sindarin words. Runes came to be used widely by races other than the Elves, and especially by the Dwarves.
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