This article is from the Calendars FAQ, by Claus Tondering firstname.lastname@example.org with numerous contributions by others.
There is no record of the 7-day week cycle ever having been broken.
Calendar changes and reform have never interrupted the 7-day cycles.
It very likely that the week cycles have run uninterrupted at least
since the days of Moses (c. 1400 BC), possibly even longer.
Some sources claim that the ancient Jews used a calendar in which an
extra Sabbath was occasionally introduced. But this is probably not