By the late 16th century, Papal influence in Europe was rapidly decreasing, although many stayed religious. Heads of states sought to increase their power within their own nation, and having another power influencing the ideas of their citizens did not appeal to many. As such, the Popes of Rome began to find their power limited, no longer able to call crusades that would sweep the continent with religious fervor. Nevertheless, on this day in 1582, Pope Gregory XIII made one last change to the world. He announced the institution of the Gregorian Calendar, which would be widely accepted as the most accurate and effective solar calendar. It consisted of seven day weeks, months of thirty or thirty-one days, and twelve month years. An exception however was February, which has twenty-eight days, except for leap years, which add on a day in order to balance the calendar. Today it is the most widely used calendar in the world, used across the Western World.