The first alphabet developed in Egypt might have been adapted from some part of the enormous system of Egyptian hieroglyphics, so it could be that the Egyptian system informed the order, too. * The ancient order was a long mnemonic device. Early users strung the letters together to correspond to the words of a mnemonic sentence or storyline. * In Semitic Writing: From Pictograph to Alphabet GR Driver touches on several explanations he’s come across, from “astral or lunar theories” to the order “representing a didactic poem” or being “based on the notation of the Sumerian musical scales.” * David Diringer, in The Alphabet: A Key to the History of Mankind, suggests that there’s no reason at all: “…it is highly probable that the matter has no particular significance...There is some appearance of phonetic grouping in the order of the letters of the North Semitic alphabet, but this may be accidental.” * The alphabet may have had a numerical component, and the order is reverse-engineered to the follow and match the numbers that the letters represented for merchants. Later civilizations hung on to the obsolete order for convenience’s sake.