In the mid-second century CE, the great Alexandrine scientist Ptolemy published his Geography, a major work in which he gave the coordinates of many cities of the ancient world. It is an important source to reconstruct the ancient geography.
The Geography, which was based on the investigations by Marinus of Tyre, also contains information about explorers who visited faraway countries. Two of these expeditions took place in the last quarter of the first century, when people from Lepcis Magna tried to organize the Transsaharan trade in wild animals like rhinoceroses.
Section 1.8.5-7 of Ptolemy's Geography is offered here in the translation by E.L. Stevenson.
[1.8.6] Each of these statements, on the face of it, is incredible, first, because the Ethiopians are not so far distant from the Garamantes as to require a three months' journey, seeing that the Garamantes are themselves for the most part Ethiopians, and have the same king;note[This is incorrect. Like many ancient authors, Ptolemy found it difficult to conceptualize the topography of Black Africa, believing that all Ethiopians (litt. "black faced people") were one nation. The Garamantes were a tribe living in Sahara; there is still an oasis named Garma.] secondly, because it is ridiculous to think that a king should march through regions subject to him only in a southerly direction when the inhabitants of those regions are scattered widely east and west,note[The route to the south was an old one, and led from the Garamantes through the Grand Erg de Bilma to Lake Chad.] and ridiculous also that he should never have made a single halt that would alter the reckoning.
[1.8.7] Wherefore we conclude that it is not unreasonable to suppose that those men either spoke in hyperbole, or else, as rustics say, "To the south," or "Toward Africa" to those who prefer to be deceived by them, rather than take the pains to ascertain the truth.