Pytheas described his travels in a work that has not survived; only excerpts remain, quoted or paraphrased by later authors, most familiarly in Strabo's Geographica, Pliny's Natural History and passages in Diodorus of Sicily's history.
Most of the ancients, including the first two just mentioned, refer to his work by his name: "Pytheas says …" Two late writers give titles: the astronomical author Geminus of Rhodes mentions τὰ περὶ τοῦ Ὠκεανοῦ (ta peri tou Okeanou), literally "things about the Ocean", sometimes translated as "Description of the Ocean", "On the Ocean" or "Ocean"; Marcianus, the scholiast on Apollonius of Rhodes, mentions περίοδος γῆς (periodos gēs), a "trip around the earth" or περίπλους (periplous), "sail around".

Scholars of the 19th century tended to interpret these titles as the names of distinct works covering separate voyages; for example, Smith's Dictionary of Greek and Roman Biography and Mythology hypothesizes a voyage to Britain and Thule written about in "Ocean" and another from Cadiz to the Don River, written about in "Sail Around".
As is common with ancient texts, multiple titles may represent a single source, for example, if a title refers to a section rather than the whole.
Presently periplus is recognized as a genre of navigational literature.
Mainstream consensus is that there was only one work, "on the Ocean", which was based on a periplus.

Diodorus did not mention Pytheas by name.
The association is made as follows: Pliny reported that "Timaeus says there is an island named Mictis … where tin is found, and to which the Britons cross."
Diodorus said that tin was brought to the island of Ictis, where there was an emporium.
The last link was supplied by Strabo, who said that an emporium on the island of Corbulo in the mouth of the river Loire was associated with the Britain of Pytheas by Polybius.
Assuming that Ictis, Mictis and Corbulo are the same, Diodorus appears to have read Timaeus, who must have read Pytheas, whom Polybius also read.
Pytheas described his travels in a work that has not survived; only excerpts remain, quoted or paraphrased by later authors, most familiarly in Strabo's Geographica, Pliny's Natural History and passages in Diodorus of Sicily's history. Most of the ancients, including the first two just mentioned, refer to his work by his name: "Pytheas says …" Two late writers give titles: the astronomical author Geminus of Rhodes mentions τὰ περὶ τοῦ Ὠκεανοῦ (ta peri tou Okeanou), literally "things about the Ocean", sometimes translated as "Description of the Ocean", "On the Ocean" or "Ocean"; Marcianus, the scholiast on Apollonius of Rhodes, mentions περίοδος γῆς (periodos gēs), a "trip around the earth" or περίπλους (periplous), "sail around".
Scholars of the 19th century tended to interpret these titles as the names of distinct works covering separate voyages; for example, Smith's Dictionary of Greek and Roman Biography and Mythology hypothesizes a voyage to Britain and Thule written about in "Ocean" and another from Cadiz to the Don River, written about in "Sail Around". As is common with ancient texts, multiple titles may represent a single source, for example, if a title refers to a section rather than the whole. Presently periplus is recognized as a genre of navigational literature. Mainstream consensus is that there was only one work, "on the Ocean", which was based on a periplus.
Diodorus did not mention Pytheas by name. The association is made as follows: Pliny reported that "Timaeus says there is an island named Mictis … where tin is found, and to which the Britons cross." Diodorus said that tin was brought to the island of Ictis, where there was an emporium. The last link was supplied by Strabo, who said that an emporium on the island of Corbulo in the mouth of the river Loire was associated with the Britain of Pytheas by Polybius. Assuming that Ictis, Mictis and Corbulo are the same, Diodorus appears to have read Timaeus, who must have read Pytheas, whom Polybius also read.
Pytheas