GREGORIAN CALENDAR or NEW STYLE, the calendar substituted for the ancient church calendar—founded on two erroneous suppositions, namely, that the year contains 365i days and that 235 lunations are exactly equal to nineteen solar years—in March 1582 by Pope Gregory XIII. It was introduced into Spain, Portugal and part of Italy the same day as at Rome; France and Germany followed and it has since been received in almost all Christian countries. For the computation of the Gre gorian calendar see CALENDAR.