The quest for the sources of the Nile had been -already since the antiquity- a major issue regarding the exploration of Africa by both locals and foreigners. This makes no surprise, if the importance of the river is taken into account, not only from a strictly economical point of view but also from a political, historical and cultural one. Since Ptolemy introduced the Mountains of the Moon, the whole issue got a more stable basis; the quest had a specific aim from then on. Those mountains, either existing or product of a false translation tantalized the researchers for ages. On the other hand, the difficulties of such a risky expedition helped the Ptolemaic authority remain unchanged within the cartographic depictions long after the Age of Discovery. This paper aims only to outline the framework of this great issue, highlighting also a few points and proposing answers to questions which, though not of high priority, are really important: Did Ptolemy himself have first-hand geographic knowledge of that area? Did the ancient people of that part of Africa have adequate knowledge of such a complicated hydrological phenomenon? Was the Ptolemaic text in its original form when Planoudis discovered it, or had it got updated with fresh geographic knowledge through the ages?