I mean, if today i.e. is Sunday then someone long time ago should have said “Today will be Sunday” for the first time in a period from today that is multiple of seven. I was assuming that it was Pope Gregory XIII in October 1582, but looks like he is not. I failed in googling and duckduckgoing out the answer, so I ask for Lemmy’s collective wisdom!
EDIT: so question is not about the origin of 7-day week and sequence of weekday names, but about the exact reference point (day) of today’s weekday countdown. From when have people stopped adding or ommiting any adjustment ‘out-of-week’ days (like in Babylon or Rome) and kept counting to seven till today? In other words, there should be a point exactly N x 7 days ago from which the 7-day countdown has not been interrupted. Or at least the earliest known day in history that everyone on Earth agreed upon as a reference point
EDIT 2: Solved by https://lemmy.world/comment/1852458 Thanks everyone!
Our idea of a week can probably be traced back directly to early Israelite religion. There’s good evidence of a 7-day cycle by the 6th century BCE, maybe as early as the 9th. They cared which day was which because the 7th day was a holy day of rest (still practiced as Shabbat), matching up with the supposed final day of creation. Jews have been keeping this practice for a very long time, so I would guess that we’re still aligned with the days the ancient Israelites were following that they thought matched up with the days of creation. Unfortunately, the exact nature of what day they decided was which is lost to time.