And God blessed the seventh day, and sanctified it:
Genesis 2:3
The ancients acknowledged the Jewish 7th day is what we call "Saturday"
".... there is evidence that the Jewish Sabbath was identified with Saturn’s day in the first century BC. Dio Cassius tells of the Roman attack on the temple in Jerusalem, a success on Saturn’s day because the defenders would not fight on that day. There is a suggestion in the writings of the Roman poet Tibullus (who died in 18 BC) that the Jewish people were thought to be Saturn worshippers."
CMI
And by the 2-3rd century some Christians were already attempting to make excuses to arrogantly transfer the solemnity of the 7th day Sabbath of God to the 1st day of the week
"The planetary weekday names were later accepted by the Roman branch of the church, and hence ‘Christianised’. Jerome says of Psalm 118:24, ‘Why is it called the Lord’s day? Because on it He ascended victoriously to His Father. But if the Gentiles called it the Sun’s day, we gladly admit it. For in this day the light of the world rose, on this day the sun of righteousness rose."
CMI