January is the first month of the Gregorian calendar. It was named after Janus, the Roman god of
all beginnings. January replaced March as the first month of the Roman year no later than 153 BCE
JANUS
in Roman religion, the animistic spirit of doorways (januae) and archways (jani). Janus and the nymph Camasene were the parents of Tiberinus, whose death in or by the river Albula caused it to be renamed Tiber.

The worship of Janus traditionally dated back to Romulus and a period even before the actual founding of the city of Rome. There were many jani (i.e., ceremonial gateways) in Rome; these were usually freestanding structures that were used for symbolically auspicious entrances or exits. Particular superstition was attached to the departure of a Roman army, for which there were lucky and unlucky ways to march through a janus. The most famous janus in Rome was the Janus Geminus, which was actually a shrine of Janus at the north side of the Forum. It was a simple rectangular bronze structure with double doors at each end. Traditionally, the doors of this shrine were left open in time of war and were kept closed when Rome was at peace. According to the Roman historian Livy, the gates were closed only twice in all the long period between Numa Pompilius (7th century BC) and Augustus (1st century BC).

Some scholars regard Janus as the god of all beginnings and believe that his association with doorways is derivative. He was invoked as the first of any gods in regular liturgies. The beginning of the day, month, and year, both calendrical and agricultural, were sacred to him. The month of January is named for him, and his festival took place on January 9, the Agonium. There were several important temples erected to Janus, and it is assumed that there was also an early cult on the Janiculum, which the ancients took to mean “the city of Janus.”

Janus was represented by a double-faced head, and he was represented in art either with or without a beard. Occasionally he was depicted as four-faced—as the spirit of the four-way arch.

GREGORIAN CALENDAR
also called New Style Calendar

solar dating system now in general use. It was proclaimed in 1582 by Pope Gregory XIII as a reform of the Julian calendar.

By the Julian reckoning, the solar year comprised 365 1/4 days; the intercalation of a “leap day” every four years was intended to maintain correspondence between the calendar and the seasons. A slight inaccuracy in the measurement (the solar year comprising more precisely 365 days, 5 hours, 48 minutes, 45.25 seconds) caused the calendar dates of the seasons to regress almost one day per century.

Although this regression had amounted to 14 days by Pope Gregory's time, he based his reform on restoration of the vernal equinox, then falling on March 11, to the date (March 21) it had in AD 325, the time of the Council of Nicaea, and not on the date of the equinox at the time of the birth of Christ, when it fell on March 25. The change was effected by advancing the calendar 10 days after Oct. 4, 1582, the day following being reckoned as October 15.

The Gregorian calendar differs from the Julian only in that no century year is a leap year unless it is exactly divisible by 400 (e.g., 1600, 2000). A further proposed refinement, the designation of years evenly divisible by 4,000 as common (not leap) years, will keep the Gregorian calendar accurate to within one day in 20,000 years.

Within a year the change had been adopted by the Italian states, Portugal, Spain, and the German Catholic states. Gradually, other nations adopted the Gregorian calendar: the Protestant German states in 1699; England and its colonies in 1752; Sweden in 1753; Japan in 1873; China in 1912; the Soviet Union in 1918; and Greece in 1923. Islamic countries tend to retain calendars based on Islam.
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