The only guidance to date or authorship must be found in the Periplus itself.
Hippalus' discovery of the sea-route to India, described in § 57, is fixed by Vincent at about 47 A. D.
Vincent reasons from Pliny's account (VI, 24) of the accidental journey of a freedman of Annius Plocamus who had farmed from the Treasury the revenues arising from the Red Sea. This freedman was carried away by a gale and in fifteen days drifted to Ceylon, where he was hospitably received and after a stay of six months returned home; after which the Ceylonese kings sent an embassy to Rome. Pliny says that this occurred during the reign of Emperor Claudius, which began in the year 41. The discovery of Hippalus must have come very soon after. (The first question suggested by this story is, what the freedman was doing outside the Straits of Bab-el-Mandeb and from whom Annius Plocamus farmed the revenues. As to this Pliny is silent. Can it have been the friendly Abyssinians, or were the Greek colonies in Arabia still in existence?)
The discovery of Hippalus, described in § 57, seems to have occurred not long before the author of the Periplus made his voyage. He evidentally feels a deep respect for the discoverer, and goes on to say that "from that time until now" voyages could be made directly across the ocean by the monsoon.
Pliny has but a passing reference to Hippalus, suggesting that between 73 and 77 A. D. when he was writing, the memory of the discoverer had faded somewhat from view.
Assuming 50 A. D. as a date earlier than that which this Periplus can not have been written, we must look next for a limit on the other side.
In § 38 is mentioned "the sea-coast of Scythia" around the mouth of the Indus, and the metropolis of Scythia, Minnagara, which was "subject to Parthian princes at war among themselves."
In § 41 is mentioned another city Minnagara, which, as indicated in the notes, is simply the Hindu name for "city of the invaders".
§ 47 is mentioned the "very war-like inland nation of the Bactrians."
As explained in the notes, the Scythians of the Periplus are the Saka tribe, who had been driven from Eastern Turkestan by the Yueh-chi, and overran Beluchistan, the lower Indus valley, and adjacent parts of the coast of India itself. They submitted to the Parthian Kingdom, of which they formed an important part. Their southern extension under Sandares, the ruler mentioned in § 52, indicates a growing pressure from the Kushan kingdom on the north, but prior
