using systems of proto-writing as an intermediate stage before the adoption of writing proper. The "Slavic runes" (7th/8th century) mentioned by a few medieval authors may have been such a system. The quipu of the Incas (15th century), sometimes called "talking knots", may have been of a similar nature. Another example is the system of pictographs invented by Uyaquk before the development of the Yugtun syllabary (c. 1900). African Iron Age Nsibidi is a system of symbols indigenous to what is now southeastern Nigeria. While there remains no commonly accepted exact date of origin, most researchers agree that use of the earliest symbols date back between the 5th and 15th centuries. There are thousands of Nsibidi symbols which were used on anything from calabashes to tattoos and to wall designs. Nsibidi is used for the Ekoid and Igboid languages, and the Aro people are known to write Nsibidi messages on the bodies of their messengers. See also References History of writing Neolithic