This is a bit of a broad question, but it's one that woke me up last night:

Where did weeks come from and how did everyone end up agreeing on them?

Obviously, different cultures use different calendars, and obviously different cultures count the years differently. But it just seems odd that, at least in western Eurasia, everyone would be so well-agreed as to what day of the week it was and how many days a week should be. Like even if they called it different things, it's interesting that Saturday simply is Saturday, from England to Iran.

I understand that the Romans established a lot of European dating conventions, but it is also obvious this is something that existed long before the Roman Empire. I also understand the week is (very roughly) based on the phases of the moon, but did every culture agree that this was the most obvious way to divide time?

Or am I completely off-base here and the days of the week weren't consistent between cultures before modern times?