Roman calendar ancient Greek calendars; and the Gregorian calendar, which refined the Julian system to bring it into still closer alignment with the solar year and is the basis of the current international standard. Roman dates were counted inclusively forward to the next of three principal days: the first of the month (the kalends), a day less than the middle of the month (the ides), and eight days—nine, counting inclusively—before this (the nones). The original calendar consisted of 10 months beginning in spring with March; winter was left as an unassigned span of days. These months ran for 38 nundinal cycles, each
Adoption of the Gregorian calendar proved unable to keep up with the demand for copies. Catholic states such as France, the Italian principalities, Poland, Spain (along with her European and overseas possessions), Portugal and the Catholic states of the Holy Roman Empire were first to change to the Gregorian calendar. Thursday, 4 October 1582 was followed by Friday, 15 October 1582, with ten days skipped. Countries that did not change until the 18th century had by then observed an additional leap year (1700), necessitating the dropping of eleven days. Some countries did not change until the 19th or 20th century, necessitating one or two further