The Berber language having no continuous written tradition, direct evidence about the history of this language and its ancient forms are extremely rare. A systematic study of external documents (Greek-Latin and Arab) appears to be one of the few means at one's disposal for the reconstitution of the Berber diachrony. From this point of view La description de l'Afrique Septentrionale by El-Bekri appears to be a most fruitful work by the number as well as by the quality of the informations it contains about the Berber language (whole sentences, numerous translations of toponyms). The study of this text furnishes : 1) very precise and very interesting grammatical information for the history of this language; 2) plenty of lexical information (scores of identified items); 3) data about the linguistic situation in the area considered (maximal extension of the Berber language, remainders of other languages).