do you have a link for this?
Each website is some person's opinion as to how to look at evidence, and reflects upon their own world view. Their information is informative however I tend to incorporate things into my own world view which puts different interpretations on some things.
My world view takes into account Genesis scripture -- for example -- I believe God ceated the things on this planet in literal six days, and rested, blessed and sanctified the 7th, thus creating the week (which I don't think you disgree with) and I also believe that there was a flood that destroyed most all of the first creation and life started anew with Noah and his sons in the general area of Mesopotamia.
I'm only restating that because it bears on how I interprete data from websites.
Since Noah and his family were worshipers of God and knew all about Adam and Eve and creation and the Sabbath I interprete the Babylonian or Sumeriancultures in Mesopotamia as having in their back ground the TRUE story but that they preverted it into their pagan religions.
This tends to reverse the things one often reads on the internet where a popular line of thought is that Isael merely picked up their beliefs from the nations around them and modified them somewhat.
An example is
this website
which points out the seven day week comes from the first culture (after the flood) Sumeria but of course doesn't recognize that early Sumerians KNEW NOAH and the truth, and preverted it, their culture still had traces of truth mixed in with their plunge into paganism, and God called Abraham out of there to preseve the real truth.
Anyway --
Back to your question.
A simple and probably not too authoritive website on
the week
States:
"The seven-day week began with the Sumerians, who tied seven days to seven gods and planets. The Babylonians took the week and changed Sumerian gods to their Babylonian equivalents"
"Constantine believed that Mithra and Jesus were the same god. He told Christians to stop worshipping on the sabbath and worship on the day of Mithra the Invincible Sun instead. So, on Sunday, celebrate the sun!"
Here's a more authoritative website the British Mythology on Mithra
Mithra
The Sun God worshipped throughout the Roman Empire since it was first encountered by them in Persia during the reign of Emperor Nero...
Each day of the week was attributed to a planet, and the day associated with the Sun was held to be very holy.
Or how about this website:
The Iowa State Daily Article on Mithra
And the Wikipedi
On Mithraism
"It has been claimed that both Mithraism and Christianity considered Sunday their holy day, though for different reasons, although the evidence that Mithraists practiced weekly worship, any more than any other pagan religion of the time, is lacking."
And really that shouldn't surprise us -- pagans were more into celebrations and rituals then into what we as Christians know as "worship".
However, every study into Mitharism shows this is a great counterfeit of the true CHRIST.
Here's a unitarian
website on Mitharism and Constantine