His year in office was marked by Athens' official adoption of the Ionic alphabet.
[1] Although some Athenian inscriptions from before Eucleides' archonship already used the Ionian alphabet and others use the old Attic alphabet after it, the majority reflect the switch and Eucleides' archonship is thus an important milestone for dating Athenian inscriptions.
It was probably connected to political efforts to end civil strife and reform the constitution in the aftermath of the Athenian defeat in the Peloponnesian War.
[1] Armand D'Angour proposes that the Ionic alphabet had been associated with aristocratic oligarchs in late fifth century BC Athens and that its adoption as the official alphabet was part of a policy of reconciliation by victorious Athenian democrats after they overthrew the short-lived oligarchic governments of the Four Hundred and the Thirty Tyrants.
He also suggests that the archon Eucleides is identical with a secretary who was responsible for having a decree (IG I3 110) inscribed in the Ionic alphabet in 408/7 BC and with a Eucleides mentioned in Aristotle's Poetics (1458b5-15) as having criticised poets who changed the vowel length to fit poetic meters.