http://www.torah.org/qanda/seequanda.php?id=58 The Romans prohibited declaring the new moon, prohibited Hillel II, he fixed Sabbath on Saturday.

and thus the "fixture" of His Sanctuary, the proclamation of "The New Moon is Consecrated" according to the fourth commandment, was "was cast down"

http://www.macquirelatory.com/Authority%20and%20Power.html A short history on Hillel II changing and adopting the roman calendar Saturday, forsaking the lunar based wee