The letters between Sparta and Judaea preserved in 1 Maccabees and Josephus’ Antiquities have generated considerable scholarly discussion. Only Josephus’ version of Areus’ letter to Onias includes information about its courier Demoteles, its ‘square’ script and the image on its seal. Comparison with contemporary Hellenistic epigraphical evidence suggests that these elements are archival metadata rather than parts of the original letter or Josephan inventions. Similar clauses attested in documents inscribed in several Hellenistic cities are remnants of archival processes, and the presence of such details in Josephus’ version of Areus’ letter suggests that it derives from an independent source and never underwent the translation process so evident in the Maccabean versions. This strengthens the case for authenticity.