Semitic scripts apparently derive from "Proto-Sinaitic", a script of which only 31 inscriptions (plus 17 doubtful) are known. It is thought by some researchers that the original source of this script was the Egyptian hieratic script, which by the late Middle Kingdom (about 1900) had added some alphabetic signs for representing the consonants of foreign names. Egyptian activity in Sinai was at its height at that time. A similar idea had been suggested many years previously.