The Julian and Gregorian calendar reforms did not change the day of the week. As a calibrating norm, you can use the Hebrew calendar, which maintained a 7-day w

The Julian and Gregorian calendar reforms did not change the day of the week. As a calibrating norm, you can use the Hebrew calendar, which maintained a 7-day week as long as the calendar has existed. The 7-day week of the Hebrews remained in sync with the calendars of Babylon and Rome, and continues to remain in sync the modern calendars today. While there were at times questions regarding which day of the month any given day was, especially during the Babylonian Captivity, there was never a question regarding what day of the week it was. When the Jews in Babylon returned to Israel, they found their calendar to still be in sync with the Jews who were left behind in Israel. Therefore, it is safe to say that in the modern era, the day of the week has always been consistent, and seems to be consistent as far back as we have any records.