(The calendar which we have in use today is the Gregorian calender. The calendar has been changed twice in its history, but never was the order of the days of the week changed.
The Julian [named after Julius Caesar] calender calendar was introduced about the 7th century B.C. But, the Julian calendar was 11 minutes and 14 seconds longer than
the solar year. So, in 1582 the vernal equinox eccured 10 days early and church holidays did not match their appropiate seasons. Pope Gregory XIII issued a decree to drop 10 days from the calendar . Since this change, it has been called the Gregorian calendar. When the Gregorian calendar was adopted in Britain in 1752, another correction was found to be necessary. The day after Sept. 2, 1752, became Sept. 14. In both of these instances only the number of the days was changed. Never was the order of the days of week disturbed. So, consequently the Sabbath still falls on Saturday and always has.)

Encyclopedia, Vol 9, p. 251, article Lilius: "Thus every imaginable proposition was made, only one idea was never mentioned; the abandonment of the 7- day week."

Catholic Encyclopedia, Vol 3, p. 740, article Chronology: "It is to be noted that in the Christian period, the order of days in the week has never been interrupted. Thus, when Gregory xiii reformed the calendar in 1582, Thursday 4 October was followed by 15 October, Friday. So in England in 1752 wednesday 2 September, was followed by Thursday, 14 September."