From the longer Wikipedia page .
Horapollo (from Horus Apollo, Ὡραπόλλων) is the supposed author of a treatise on Egyptian hieroglyphs, extant in a Greek translation by one Philippus, titled Hieroglyphica, dating to about the 5th century.
There were two persons in the 5th century AD who were so referred to, a priest and a grammarian/dramatists, to whom the 'Hieroglyphica' has been attributed by most 16th-century editors,
The text of the Hieroglyphica consists of two books, containing a total of 189 explanations of Egyptian hieroglyphs. The books profess to be a translation from an Egyptian original into Greek by a certain Philippus, of whom nothing is known. The inferior Greek of the translation, and the character of the additions in the second book point to its being of late date; some have even assigned it to the 11th century. The text was discovered in 1419 on the island of Andros, and was taken to Florence by Cristoforo Buondelmonti (it is today kept at the Biblioteca Laurenziana, Plut. 69,27). By the end of the 15th century, the text became immensely popular among humanists, with a first printed edition of the text appearing in 1505, translated into Latin in 1517 by Filippo Fasanini, initiating a long sequence of editions and translations. From the 18th century, the book's authenticity was called into question, but modern Egyptology regards at least the first book as based on real knowledge of hieroglyphs, although confused, and with baroque symbolism and theological speculation, and the book may well originate with the latest remnants of Egyptian priesthood of the 5th century.
This approach of symbolic speculation about hieroglyphs (many of which were originally simple syllabic signs) was popular during Hellenism, whence the early Humanists, down to Athanasius Kircher, inherited the preconception of the hieroglyphs as a magical, symbolic, ideographic script. Though a very large proportion of the statements seem absurd and cannot be accounted for by anything known in the latest and most fanciful usage, there is ample evidence in both books, in individual cases, that the tradition of the values of the hieroglyphic signs was not yet extinct in the days of their author.