(Πάππος), of Alexandria, the name of one of the later Greek geometers, of whom we know absolutely nothing, beside his works, except the fact that Suidas states him to have lived under Theodosius (A. D. 379-395). From an epigram of the second century, or a little later, in which one Pappus is lauded, Reiske thought that this must be the geometer, who ought, therefore, to be placed in the latter half of the second century. And Harless remarks, in confirmation, that of all the authors named by Pappus, no one is known to have flourished later than the second century. This is but poor evidence, and, on the other hand, the authority of Suidas is by no means of the first order on a point of chronology. We may, therefore, look to other sources of probability, and the only one we can find at all to the purpose is as follows.
Pappus has left a short comment upon a portion of the fifth book of Ptolemy's Syntaxis: or rather of the comment which Suidas states him to have written upon four [*](* This portion is on the fifth book: perhaps the four books were not the first four books.) books, nothing is left except a small portion which Theon has preserved and commented on (Syntaxis, Basle, 1538, p. 235 of Theon's Commentary). Now Eutocius mentions Theon and Pappus in the same sentence, as commentators on Ptolemy; and puts them thus together in two different places. This is some presumption against Pappus having been nearly a contemporary of Ptolemy, and in favour of his standing in that relation to Theon. A commentator generally takes an established author, except when the subject of comment is itself a comment, and then he generally takes his own contemporaries. And moreover, those writers who are often named together are more likely than not to be near together in time. The point is of some importance; for Pappus is our chief source of information upon the later history of Greek geometry. It makes much difference as to the opinion we are to form on the decay of that branch of learning, whether the summary which he gives is to be referred to the second or the fourth century. If he lived in the fourth century, it is a very material fact that he could not find one geometer in the two preceding centuries whom he then considered as of note.
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