Early writing systems—in Mesopotamia, Egypt, China, and later in Mesoamerica—were pictographic at the outset, employing a picture per word or, in some cases, combining two or more pictures to represent more complex words. These symbols were not related to a particular language and its sounds but might be usable by another language, just as today’s universal road and toilet signs may be comprehensible whether one speaks English, Arabic, or Korean. This was true, also, of the earliest symbols employed in the systems we call Linear A and Linear B.
But though pictographs may be drafted to represent nouns and fairly low numerals (and were therefore admirably suited to the work of ancient accountants, who could confine themselves to counting the number of chariots and javelins in the armory and the number of horses in the stables), they are less serviceable in representing the multiple forms of a verb and begin to disintegrate altogether under the weight of such linguistic complications as subordinate clauses. So these ancient systems soon added other, more arbitrary signs to represent more accurately the actual labyrinth of language, eventually introducing even symbols that represented some of the syllabic sounds of a specific language. The final network of symbols was a combination of pictographs, considerably stylized and simplified by generations of scribes, and other complicated signs and syllabaries. These hundreds, sometimes thousands, of separate symbols could be mastered only by those who had years to devote to the study. Such cumbersome writing systems became the fuel on which their civilizations ran—the oil of the ancient world. If you participated in ownership, you had it made in the shade. Otherwise, according to Claude Lévi-Strauss, the main function of such systems was "to facilitate the enslavement of other human beings"—literacy as oppression.
Though we don’t know who thought of it, we know where the idea of an alphabet came from: the Levant, that small corridor of coast running from Syria to the Sinai and encompassing Lebanon and Israel-Palestine. The first alphabet was, in the main, a borrowing from the underutilized syllabaries hidden away in the vast network of Egyptian hieroglyphs. Like most inventions, this one probably evolved in several stages and was helped along by more than one inventor. But by the middle of the second millennium [B.C.E.], we find a language being written on stones in the Sinai that is neither pictographic nor strictly syllabic, the alphabetic precursor of written Phoenician-Canaanite-Hebrew. This primitive alphabet came to the Greeks probably by way of Phoenician merchants, whose welcome ships, loaded with metals and such exotic materials as the precious red-purple cloth of Phoenicia, plied the whole of the Mediterranean littoral.
The Greeks added vowels to the Semitic consonants and set this list of pronunciation symbols in an unvarying order, giving us the alphabet (alpha and beta being the first two letters), on which the Romans would subsequently make their own revision—and so bestow on us the very symbols in which [this web site is] printed.
— Thomas Cahill, Sailing the Wine-Dark Sea, pp. 55-57
I have substituted the words “web site” in place of the author’s “book”.