In ancient Greek dating format, does the month or day come first in order? In other words, if ancient Greeks were discussing a specific date using the Attic lunisolar calendar, how would they order their statement. If they were saying the 12th of Hekatombaion, would Hekatombaion deutéra mesoúntos be correct? Or does the day come first, and then month, like deutéra mesoúntos Hekatombaion?

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Very crudely, in the Attic lunisolar calendar, the day belongs to the month (in Genitive, possessive), and word order is not important. So, Ἑκατομβαιῶνος δευτέρα μεσοῦντος and δευτέρα μεσοῦντος Ἑκατομβαιῶνος are equivalent. It's like "July's 3rd day of waxing" or else the 3rd day of July.

The system is sort of as in English, at first, all the way to day 19:

1 Ἑκατομβαιῶνος νουμηνία‎ [new moon]

2 Ἑκατομβαιῶνος δευτέρα ἱσταμένου [2nd day of waxing]

3 Ἑκατομβαιῶνος τρίτη ἱσταμένου

4 Ἑκατομβαιῶνος τετάρτη ἱσταμένου

5 Ἑκατομβαιῶνος πέμπτη ἱσταμένου

6 Ἑκατομβαιῶνος ἕκτη ἱσταμένου

7 Ἑκατομβαιῶνος ἑβδόμη ἱσταμένου

8 Ἑκατομβαιῶνος ὀγδόη ἱσταμένου

9 Ἑκατομβαιῶνος ἐνάτη ἱσταμένου

10 Ἑκατομβαιῶνος δεκάτη ἱσταμένου [10th day of waxing]

11 Ἑκατομβαιῶνος ἑνδεκάτη [plain 11th: gibbous]

12 Ἑκατομβαιῶνος δωδεκάτη

13 Ἑκατομβαιῶνος τρίτη καὶ δεκάτη

Ἑκατομβαιῶνος τετάρτη καὶ δεκάτη

Ἑκατομβαιῶνος πέμπτη καὶ δεκάτη

Ἑκατομβαιῶνος ἕκτη καὶ δεκάτη

Ἑκατομβαιῶνος ἑβδόμη καὶ δεκάτη

Ἑκατομβαιῶνος ὀγδόη καὶ δεκάτη

19 Ἑκατομβαιῶνος ἐνάτη καὶ δεκάτη

20 Ἑκατομβαιῶνος δεκάτη προτέρα‎ [contrast to its mirror image below; go figure... The 21st is the "latter", but this one is the "former". Why not the 20th? I plead incomprehension.]

[Then, reverse counting in anticipation of launch to nothingness:]

21 Ἑκατομβαιῶνος δεκάτη ὑστέρα‎ [10th day of waning in reverse counting]

22 Ἑκατομβαιῶνος ἐνάτη φθίνοντος‎

23 Ἑκατομβαιῶνος ὀγδόη φθίνοντος‎

24 Ἑκατομβαιῶνος ἑβδόμη φθίνοντος‎ [7th from the end of waning]

25 Ἑκατομβαιῶνος ἕκτη φθίνοντος‎

26 Ἑκατομβαιῶνος πέμπτη φθίνοντος‎

27 Ἑκατομβαιῶνος τετάρτη φθίνοντος‎

28 Ἑκατομβαιῶνος τρίτη φθίνοντος‎

29 Ἑκατομβαιῶνος δευτέρα φθίνοντος‎ [second from the end of waning]

30 Ἑκατομβαιῶνος ἔνη καὶ νέα [former and new: you can't see either]

You appear to know Ἑκατομβαιῶνος δωδεκάτη might be Ἑκατομβαιῶνος δευτέρα μεσοῦντος, which makes neater sense today. I've seen it. So the middle 10 (ahem! 9) days (gibbous/full) might go this way.

Given the Genitive for the month to which each day belongs, word order is immaterial. So, equivalently, " ἐκ Τροιζῆνος ἀφικέσθαι τῇ ὀγδόῃ τοῦ Ἑκατομβαιῶνος" [Plut. Thes. 36.3]...

There are variants for the numbers, too, so, e.g., ἑβδόμη καὶ δεκάτη is equivalent to ἑβδόμη ἐπὶ δέκα.

Let me stick in a silly figure as a summary of the month, splitting it in three parts as discussed, enter image description here

  • 2
    I studied this a long time ago. If I remember correctly, the 20th is the day that is omitted in 29-day months. (The lunar cycle is approximately 29.5 days, so the months have 29 or 30 days, alternating). This explains (more or less) the nomenclature for the 20th and 21st.
    – fdb
    Commented Jul 7, 2021 at 14:39
  • 1
    Thanks much. This makes more sense than anything I've seen; the overflow/slop day merits a perverse name. I had thought of it as some type of residual μεσοῦντος δεκάτη, with προτέρα/ὑστέρα contrasting the two spatchcocked 10s. Commented Jul 7, 2021 at 14:49
  • Thank you Cosmas Zachos for this excellent answer, and @fdb for expanding upon it, This was very very helpful and greatly appreciated.
    – Walter
    Commented Jul 8, 2021 at 7:30

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