The cuneiform ru sign is found in both the 14th century BC Amarna letters and the Epic of Gilgamesh. As ru it is used for syllabic ru, and alphabetic 'r', or 'u'. In the I-XII Tablets of the Epic of Gilgamesh, it has specific uses showing alternate renderings besides ru; as sign no. 068, ru, 250 times, šub, 6, šup, 3, and as Sumerogram ŠUB, 1 time. In the Amarna letters, the sign is mostly used for ru, r, and u in the spelling of various words. Notably, for "bird", Akkadian language "iṣṣūru", in , (Tushratta to Pharaoh), titled "Messengers Detained and a Protest"; the messengers are referenced as "uncaged" birds, and "aren't they free to come and go as birds do?".