In J.R.R. Tolkien’s legendarium, what language is written on the One Ring?

The inscription on the One Ring is written in the Black Speech of Mordor.

The inscription begins, “Ash nazg durbatulûk,” translated as “One Ring to rule them all.” Sauron created the Black Speech for the servants of Mordor, and he used it for the Ring inscription to express the power that binds the other Rings of Power to the One Ring.

A common mix-up is confusing the language with the writing system. The words are in Black Speech, but the letters are Tengwar, a script developed by the Elf Fëanor. The Ring’s inscription is therefore an example of one language written with another culture’s script.

The inscription becomes visible when the Ring is heated. It is revealed at the Council of Elrond after Gandalf places the Ring in fire. Tolkien gave only limited vocabulary and grammar for the Black Speech compared with languages such as Quenya and Sindarin.