(Geek alert) I don't think the ancient Romans and Greeks had seven-day weeks, even though our days of the week contain references to classical deities. I've read a lot of Latin, including a lot of Cicero's dated letters, and I've never seen anyone refer to the name of a weekday. At least in Rome, the month was divided not into weeks but into sections defined by the Calends, or Kalends (whence "calendar"), the Nones and the Ides of the months. The Ides (as in "of March") fell on the 15th or the 13th or 12th, depending on the month. The nones fell on the 9th or the 7th, and the Calends (only in Roman, not Greek tradition) was the first day of the month. These "hinges" in the month defined when debts had to be paid, and I think when they had market days, which were generally days off. Business men who were out of town would get back to the city on the Ides or the Calends in order to collect from their debtors. (One Latin expression for "when hell freezes over" was "On the Greek Kalends".) Dates were calculated as how close they were to the next hinge -- so Dec 30 would be the day before the Calends of January, and March 11 would be three days before the Ides of March. The year was calculated by who was consul that year, or by how many years after 753 BC it was (the legendary year that Romulus and Remus founded the city -- on April 21).

The Romans are notorious for having had a lot of holidays but that was mostly and increasingly true during the empire, not the earlier republic. By late empire they had declared dozens of festivals and feast days, worshipping various emperors, so that they actually ended up with about 1/3d of the year off. Anyway, I am pretty sure that the seven-day-week, which is obviously Judeo-Christian, right out of Genesis, only came to the Roman world with Christianity, not earlier -- except of course in ancient Judea, modern Israel, where it originated. But even there, the Roman governors wouldn't have observed it -- they would have tolerated it, but not observed it.

Well, I warned you, I issued a Geek alert. Sometimes I just can't help myself. Old Latin teachers never die...