We publish about the first third part of the anonyma Prolegomena to Ptolemy's Almagest. This text is a kind of commentary on the first Book of Ptolemy's famous Book, commentary probably composed in a Neoplatonic circle of the fifth-sixth centuries. It is one of the latest mathematical texts of Greek Antiquity, not yet completly published. The parts I-III contain a isagogical presentation of Ptolemy's treatise, a version of a tract on isoperimetric and isepiphane figures, a chapter ont the earth's measure. Following this are several chapters on sexagesimal writing numbers and calculations, the more systematic ancient treatment transmitted to us and then a short tract on ratios composed by ratios. These parts will be published in two next issues of the same Journal.