Acarnania
A region of west-central Greece, whose people, Macrobius says, counted a year of six months.
Today: Aetolia-Acarnania, Greece
Where the months got their names
Macrobius, Saturnalia 1.12–14 (early fifth century CE), in the edition of Franz Eyssenhardt (Leipzig, 1893) · early fifth century CE; the dialogue is set in the 380s
Anni certus modus apud solos semper Aegyptios fuit. aliarum gentium dispari numero pari errore nutabat, et ut contentus sim referendo paucarum morem regionum, Arcades annum suum tribus mensibus explicabant, Acarnanes sex, Graeci reliqui trecentis quinquaginta quattuor diebus annum proprium computabant.
Only the Egyptians have always had a fixed length for the year. Among other peoples the year wavered. Their numbers differed, but they were all equally wrong. To name the custom of just a few places, the Arcadians finished their year in three months and the Acarnanians in six. The rest of the Greeks counted their year as 354 days.