Januarius	Maius	September
Februarius	Junius	October
Martius	Julius	November
Aprilis	Augustus	December

Latin words used here to designate the months of the year are adjectives. In the form given above, they modify mensis which is often omitted as in mensis Martius or mensis Aprilis. The word mensis is 3rd declension: mensis, mensis, M.

Julius was originally Quintus and Augustus was originally Sextus. Julius Caesar changed Quintus in honor of himself when he reorganized the calendar. Not to be outdone by Uncle Julius, Augustus Caesar changed the month Sextus to Augustus in honor of himself.

Kalends (Kal.) = 1st day of each month; Latin: Kalendae

Nones (Non) = 5th day except for 4 months; Latin: Nonae

Nones (Non) = 7th day in March, July, October , and May

Ides (Id) = 13th day except for 4 months; Latin: Idus

Ides (Id) = 15th day in March, July, October, and May

Romans counted both the day they started from and the day they were counting to.

E.g. , Augustus 01 Julius 31 Julius 30 Julius 29 Julius 28

1 2 3 4 5

July 28 = a d V Kal. Aug (5 days before the first of August)

(a d = ante diem)

On the day before the Kalendae, Nonae, or Idus, Romans used the word pridie which means on the day before. E.g., prid. K. means on the day before the first.

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The days of the week in Latin

Solis dies, Lunae dies, Martis dies, Mercurii dies, Jovis dies, Veneris dies, Saturni dies,

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Hours Between sunrise (solis ortus) and sunset (solis occasus). They were divided into 12 parts called horae. Length of the horae varied with the season.

Night was divided into 4 watches:

6-9 p.m. = prima vigilia 9-12 p.m. = secunda vigilia

12-3 a.m. = tertia vigilia 3-6 a.m. = quarta vigilia 

Early Roman calendar