Pytheas was a central source of information on the North Sea and the subarctic regions of western Europe to later periods, and possibly the only source. The only ancient authors we know by name who certainly saw Pytheas' original text were Dicaearchus, Timaeus, Eratosthenes, Crates of Mallus, Hipparchus, Polybius, Artemidorus and Posidonius. Notably the list does not include Strabo or Tacitus, though Strabo discussed him and Tacitus may likely have known about his work. Either of the two could have known him through other writers or have read his work in the original.