HISTORY OF CALENDARS
The history of calendars covers practices with ancient roots as people created and used various methods to keep track of days and larger divisions of time. Calendars commonly serve both cultural and practical purposes and are often connected to astronomy and agriculture. (Source)
Wurdi Youang , Australia (~9000+ BCE)
A series of stones, located to the west of the arrangement's western apex, mark the positions of the setting sun at the equinoxes and solstices. A survey study shows that these alignments are accurate to within a few degrees. Additionally, the straight sides of the arrangement, which diverge from its eastern apex, also indicate the setting position of the sun at the solstices to within a few degrees. At the equinoxes, the sun sets over the three prominent stones at its apex. (Source)
Warren Field , Scotland (~8000 BCE)
Warren Field is the location of a Mesolithic calendar monument built about 8,000 BCE. It includes 12 pits believed to correlate with phases of the Moon and used as a lunisolar calendar. It is considered to be the oldest lunisolar calendar yet found. It is near Crathes Castle, in the Aberdeen-shire region of Scotland, in the United Kingdom. It was originally discovered from the air as anomalous terrain by the Royal Commission on the Ancient and Historical Monuments of Scotland. It was first excavated in 2004. (Source)
Calendar of Nippur , Sumeria (~4000 BCE)
The civil lunisolar calendar was used contemporaneously with an administrative calendar of 360 days, with the latter used only in fiscal or astronomical contexts. The lunisolar calendar descends from an older Sumerian calendar used in the 4th and 3rd millennia BCE.
The civil lunisolar calendar had years consisting of 12 lunar months, each beginning when a new crescent moon was first sighted low on the western horizon at sunset, plus an intercalary month inserted as needed, at first by decree and then later systematically according to what is now known as the Metonic cycle. (Source)
Babylonian Calendar , Mesopotamia (~2000BCE)
The Babylonian calendar was a lunisolar calendar used in Mesopotamia from around the second millennium BCE until the Seleucid Era (294 BCE), and it was specifically used in Babylon from the Old Babylonian Period (1780 BCE) until the Seleucid Era. The civil lunisolar calendar was used contemporaneously with an administrative calendar of 360 days, with the latter used only in fiscal or astronomical contexts. The lunisolar calendar descends from an older Sumerian calendar used in the 4th and 3rd millennia BCE. (Source)
Egyptian Calendar , Egypt (~1300BCE)
The ancient Egyptian calendar – a civil calendar – was a solar calendar with a 365-day year. The year consisted of three seasons of 120 days each, plus an intercalary month of five epagomenal days treated as outside of the year proper. Each season was divided into four months of 30 days. These twelve months were initially numbered within each season but came to also be known by the names of their principal festivals. Each month was divided into three 10-day periods known as decans or decades. It has been suggested that during the Nineteenth Dynasty and the Twentieth Dynasty the last two days of each decan were usually treated as a kind of weekend for the royal craftsmen, with royal artisans free from work. (Source)
Assyrian Calendar , West Asia (~300BCE)
Historically and also in some sources in the modern day, Assyrians dated their calendar according to the Seleucid reckoning, beginning on the first day of Tešrīn Qḏīm in 312 BC.
The modern Assyrian calendar, however, uses a different reckoning: 4750 BC was set as its first year in the 1950s, based on a series of articles published in the Assyrian nationalist magazine Gilgamesh; the first came in 1952 and written by Nimrod Simono and dealt with the Akitu festival, then an article by Jean Alkhas in 1955 (April, issue 34) fixed the year 4750 BC as the starting point. Alkhas referenced his information to a French archaeologist, whom he did not name, as stating that a cuneiform tablet dating to 4750 BC mentioned the year of the calming of the great flood and beginning of life. (Source)
Vikram Samvat , India (~56BCE)
The Vikram Samvat has been used by Hindus and Sikhs. One of several regional Hindu calendars in use on the Indian subcontinent, it is based on twelve synodic lunar months and 365 solar days. The lunar year begins with the new moon of the month of Chaitra. This day, known as Chaitra Sukhladi, is a restricted (optional) holiday in India. A number of ancient and medieval inscriptions used the Vikram Samvat. Although it was purportedly named after the legendary king Vikramaditya Samvatsara (‘Samvat’ in short), ‘Samvat’ is a Sanskrit term for ‘year’. Emperor Vikramaditya of Ujjain started Vikram Samvat in 57 BC and it is believed that this calendar follows his victory over the Saka in 56 B.C. (Source)
Coligny Calendar , Rome (~200BCE)
The Coligny calendar is a bronze plaque with an inscribed calendar, made in Roman Gaul in the 2nd century CE. It lays out a five-year cycle of a lunisolar calendar, each year with twelve lunar months. An intercalary month is inserted before each 2.5 years. The lunar phase is tracked with exceptional precision, adjusted when necessary by a variable month, and the calendar uses the 19-year Metonic cycle to keep track of the solar year. It is the most important evidence for the reconstruction of an ancient Celtic calendar. (Source)
Pre-Julian Roman Calendar , Rome (~200BCE)
According to most Roman accounts, their original calendar was established by their legendary first king Romulus. It consisted of ten months, beginning in spring with March and leaving winter as an unassigned span of days before the next year. These months each had 30 or 31 days and ran for 38 nundinal cycles, each forming a kind of eight-day week and ending with religious rituals and a public market. This fixed calendar bore traces of its origin as an observational lunar one. In particular, the most important days of each month —its kalends, nones, and ides— seem to have derived from the new moon, the first-quarter moon, and the full moon respectively. (Source)
Julian Calendar , Rome (45BCE)
The Julian calendar was proposed in 46 BC by (and takes its name from) Julius Caesar, as a reform of the earlier Roman calendar, which was largely a lunisolar one. It took effect on 1 January 45 BC, by his edict. The Julian calendar has two types of years: a normal year of 365 days and a leap year of 366 days. They follow a simple cycle of three normal years and one leap year, giving an average year that is 365.25 days long. That is more than the actual solar year value of approximately 365.2422 days (the current value, which varies), which means the Julian calendar gains one day every 129 years. In other words, the Julian calendar gains 3.1 days every 400 years. (Source)
Gregorian Calendar , Most of World (1582)
The Gregorian calendar is the calendar used in most parts of the world. It went into effect in October 1582 following the papal bull Inter gravissimas issued by Pope Gregory XIII, which introduced it as a modification of, and replacement for, the Julian calendar. The principal change was to space leap years differently so as to make the average calendar year 365.2425 days long, more closely approximating the 365.2422-day 'tropical' or 'solar' year that is determined by the Earth's revolution around the Sun. (Source)