Today (or the coming day at least) marks the Ides of Sextilis/August (depending on if you prefer the pre-imperial name for the month).
So I thought it would be prudent to talk a little bit about the Ides, and what it means. I'm going to be getting a teensy bit ahead of myself, as far as talking about Roman religious practices go, but I'll get to the specifics of that soon enough.
The Romans had a largely set and ordered calendar for the year, starting in March, periodically with an intercalary month inserted in. Under the reforms of dictator Gaius Julius Caesar, this was redone so that February had a leap day every four years, and the calendar began in January. But the monthly order of days went largely the same.
Each month begins on the Kalends, with the Ides roughly in the middle of the month, and the Nones in between the two. More than any other day of the month, these three were of special religious significance. They marked the opening stages of the month and established its cycle, and there were no public festivals before the Nones, after which the monthly holidays were announced by the priests. It was especially on these days that gods of the household were honoured, as well as the chief gods of the Roman pantheon: Jupiter and Juno.
The day immediately after any of these three was considered a dark and unlucky day, dies atri, where candles or lamps were not ritually lit, where any private religious ceremonies abstained from offerings, where the names of the gods went unspoken, and where public religious ritual was not conducted. There were very rare exceptions, but for the most part these traditions held sway.
The Kalends, as said, was on the first of the month. The Nones was held on either the 5th or 7th, and generally followed the First Quarter of the moon. The Ides was held on the 13th or 15th of the month, typically on the day after the full moon. Like most calendars in the ancient world, the original Roman calendar was at least partially lunar. This aspect, however, decreased as the Romans gradually transformed their time-keeping into a fixed solar calendar.
The Ides were given special status as a regular, cyclical Feriae Jovis, or a public festival of Jupiter. In both private and public worship, offerings would be made to the chief of the gods for prosperity and safety. This day, I will do my part in making a private offering to Jove.
