Ancient d20 die emerges from the ashes of time
Many centuries before Dungeons & Dragons was even a glimmer in the eye of Gary Gygax, ancient Egyptians were rolling a d20 die.
Twenty-sided die (icosahedron) with faces inscribed with Greek letters Period: Ptolemaic Period–Roman Period Date: 2nd century B.C.–4th century A.D. Geography: Country of Origin Egypt
Did the Ancient Egyptians really use 20-sided dice, or was this just a one time thing or a fake?
The Egyptians and other cultures really did use twenty-sided dice as evidenced by studies and artifacts, such as the one at the Met.
For example, "A Demotic Inscribed Icosahedron from Dakhleh Oasis" by Martina Minas-Nerpel published in the The Journal of Egyptian Archaeology in 2007 (Vol. 93, pp. 137-148), describes "a unique icosahedron found at Qaret el-Muzzawaqa in the 1980s and now housed in the New Valley Museum at Kharga" (pictured above). Mina-Nerpel writes,
It probably dates to the first century ad. In contrast to other icosahedra known from Graeco-Roman Egypt, this one is not inscribed with Greek or Latin letters or numbers, but with 20 Egyptian divine names in Demotic, thus adapting Egyptian concepts to a Greek form [...] The polyhedron was presumably used in an oracular procedure intended to establish which deity would provide help to the petitioner.
She goes on to cite examples of Egyptian icosahedra including: three "made of steatite or faience, inscribed with Greek letters" in Cairo and Paris museums, "four polyhedra from Egypt with Greek letters made of faience, serpentine, steatite, or calcite" housed in the British Museum, "a faience icosahedron inscribed with Greek letters" sold on the art market, and a rock crystal icosahedron "inscribed with Latin letters and Roman numerals" at the Louvre.
These are described (or "published" in other words) in the literature and regarded as authentic by scholars and collectors.
For more information you can begin with a chapter by W.J. Tait called "Dicing with the Gods" in Egyptian Religion, edited by W. Clarysse, A. Schoors, and H. Willems (Leuven: Peeters, 1998).
It is worth mentioning that Platonic solids (of which icosahedron is one) were also known to the Greeks, at least as far back as 300 BC. Euclid attributes the discovery of the icosahedron to Theaetetus. (See "The Discovery of Regular Solids" by William C. Waterhouse in Archive for History of Exact Sciences, Vol. 9, No. 3, 30.XII.1972).
During the Ptolemaic Period [305 BC–30 BC], there was Greek rulership over the land of Egypt.
The Greeks were familiar with icosahedra. They were described by Plato, a 5th century BC Greek philosopher and mathematician, as one of the Platonic Solids.
The earliest icosahedra dice found in Egypt had Greek inscriptions. For example:
This die, now in The Met museum, was acquired between 1883 and 1906 by Reverend Chauncey Murch while conducting missionary work in Egypt.
Here's another example of a Greek-inscribed die from Egypt.
The example presented in another answer, based on the A Demotic Inscribed Icosahedron from Dakhleh Oasis is from a later period - the first century AD.
It has a Demotic inscription, which suggests it is post-Ptolemaic. It appears to be a poor imitation of a regular icosahedra.
There is no prior record of Egyptians (as in native Egyptian people prior to Greek conquests on their lands) using or studying on geometric ideas relative to icosahedra.
The Egyptian-inscribed dice that are found in Egypt are obviously leftover heritage from the Ptolemaic-era Greeks.
In conclusion, Ancient Egyptians - that is Egypt before about 330 BC - did not have icosohedra dice. They were introduced to Egypt in the Classical Antiquity period by the Greeks.
