History of calendars facts for kids
Have you ever wondered how people kept track of time long ago? The history of calendars explores how humans created and used different ways to measure days, months, and years. Calendars are super important for cultures and daily life. They often connect to studying the stars (astronomy) and farming.
Archaeologists have found ways people kept time that go back to prehistoric times. These methods are at least as old as the Stone Age. Most early societies used natural units for timekeeping. These included the day, the solar year, and the moon's cycle (lunation). Calendars are clear systems used for keeping track of time. The first official calendars appeared in the Bronze Age. They developed alongside writing in the ancient Near East.
The Yoruba people of West Africa have one of the oldest recorded calendars. It is called Kojoda and dates back over 10,067 years as of 2025. This means its origin can be traced to about 8042 BC. In Victoria, Australia, a stone arrangement called Wurdi Youang might be over 11,000 years old. In 2013, archaeologists found evidence of a 10,000-year-old calendar system in Warren Field, Scotland. This is known as "the first Scottish calendar." The Sumerian calendar came next, followed by the Egyptian, Assyrian, and Elamite calendars.
The Vikram Samvat calendar has been used by Hindus and Sikhs. It is one of several Hindu calendars in India. It uses twelve lunar months and 365 solar days. The lunar year starts with the new moon of the month of Chaitra. This day is a special holiday in India. Many old writings used the Vikram Samvat. It was named after the legendary king Vikramaditya. The word 'Samvat' is a Sanskrit term for 'year'. Emperor Vikramaditya of Ujjain started Vikram Samvat in 57 BC. This calendar is believed to follow his victory over the Saka people in 56 BC.
More calendar systems from the ancient East appeared in the Iron Age. These were based on the Assyrian and Babylonian calendars. This includes the calendar of the Persian Empire. It later led to the Zoroastrian calendar and the Hebrew calendar.
Ancient calendars often combined lunar and solar cycles. They added extra months to keep the solar and lunar years aligned. This was usually based on observations of the sky. The Roman calendar, however, had very old parts from a 10-month solar year.
The Roman calendar was changed by Julius Caesar in 45 BC. The Julian calendar no longer relied on seeing the new moon. Instead, it followed a simple rule of adding a leap day every four years. This made the calendar month separate from the moon's cycle.
Calendars in Sub-Saharan Africa could have different numbers of days and weeks. This depended on the kingdom or tribe that created them.
In the 11th century in Persia (modern-day Iran), a calendar change happened. It was led by Omar Khayyam and announced in 1079. The length of the year was measured as 365.24219858156 days. This was incredibly accurate for its time. For example, the length of the year at the end of the 19th century was 365.242196 days. At the end of the 20th century, it was 365.242190 days.
The Gregorian calendar was introduced in 1582. It was an improvement on the Julian calendar. Today, it is used worldwide as the main calendar for everyday purposes.
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What Does "Calendar" Mean?
The word calendar comes from the calends. This was the name for the first day of the month in the Roman calendar. It is related to a Latin word meaning "to call out." This referred to calling out or announcing that the new moon had just been seen. The Latin word for "account book" was also related. This is because accounts were settled and debts were collected on the calends of each month.
The Latin term became calendier in Old French. From there, it entered Middle English as calender by the 13th century. The spelling calendar is from more modern English.
Calendars in Prehistoric Times
Many Upper Paleolithic cave paintings of animals in Europe have dots and lines next to them. Some experts think these are tally marks that show lunar months. They believe the year started at the end of winter. A special "Y" symbol might have shown important times for animal life cycles. This would make each sequence a calendar based on nature.
Many prehistoric structures are thought to have been used for timekeeping. They likely tracked the path of the solar year. This includes many large stone structures called megalithic structures. These arrangements go back far into the Neolithic period.
In Victoria, Australia, a Wurdi Youang stone arrangement might be over 11,000 years old. This idea is based on how the calendar's accuracy matches changes in Earth's orbit over time. This site is near the world's oldest known place for raising fish.
A Mesolithic arrangement of twelve pits and an arc was found in Warren Field, Scotland. It dates to about 8,000 BC. It has been called a lunar calendar and was named the "world's oldest known calendar" in 2013.
Ancient Calendars
Ancient Sumerian Calendar
The ancient Sumerian calendar is from around 2100 BC. It divided a year into 12 lunar months. Each month had 29 or 30 days. A new month began when the new moon was seen. Sumerian months did not have the same names everywhere. So, writers often called them "the first month," "the fifth month," and so on. To keep the lunar year (354 days) in line with the solar year (about 365 days), an extra month was added sometimes. This is similar to a Gregorian leap year. There were no weeks in the Sumerian calendar. Holidays and days off were usually on the first, seventh, and fifteenth of each month. There were also feast days that changed from city to city.
Babylonian and Persian Calendars
The earliest signs of Iranian calendar traditions are from the second millennium BC. This was before the prophet Zoroaster appeared. However, the first complete calendar is from the Achaemenids. Throughout history, Persians have cared a lot about calendars. They were among the first cultures to use a solar calendar. They preferred solar calendars over lunar or lunisolar ones. The sun has always been a symbol in Iranian culture. It is closely linked to stories about Cyrus the Great.
Old Persian Calendar
Old Persian writings show that early Iranians used a 360-day calendar. It was based directly on observing the sun. Days were not named. Months had two or three parts, depending on the moon's phase. Twelve months of 30 days were named after festivals or farming activities. A 13th month was added every six years. This kept the calendar in sync with the seasons.
Zoroastrian Calendar
The first calendars based on Zoroastrian beliefs appeared later in the Achaemenid period (650 to 330 BC). They changed over centuries, but month names stayed mostly the same.
The large Achaemenid Empire needed its own special Iranian calendar. One was created based on Egyptian traditions. It had 12 months of 30 days. Each day was dedicated to a yazata (a divine being). Four days each month were for Ahura Mazda, the main god. Other days were named after important spiritual beings and concepts like Fire, Water, Sun, Moon, and Justice.
Persian Calendar in the 11th Century
Toghril Beg, who founded the Seljuq dynasty, made Esfahan his capital. His grandson Malik-Shah ruled there from 1073. Malik-Shah and his vizier invited Khayyam to Esfahan to build an observatory. Other top astronomers also came. For 18 years, Khayyam led these scientists. They created excellent work. During this time, Khayyam helped create astronomical tables. He also worked on calendar reform in 1079.
Khayyam measured the length of the year as 365.24219858156 days. This was an incredibly precise measurement for his time. For comparison, the length of the year at the end of the 19th century was 365.242196 days. Today, it is 365.242190 days.
Classical Greek Calendars
The Greeks, even in the time of Homer, knew about dividing the year into twelve lunar months. However, they did not mention adding extra months or days then. Besides dividing months into days, they also divided them based on the moon's phases. The first day, or new moon, was called Noumenia. The month that started the year, and the names of the months, were different in various Greek states. In some places, months were just numbered, like the first, second, or third month.
The ancient Athenian calendar was a lunisolar calendar. It had 354-day years. It consisted of twelve months that alternated between 29 or 30 days. To keep the calendar aligned with the solar year (about 365 days), an extra month was added in certain years. This happened in years 3, 6, 8, 11, 14, 17, and 19 of a 19-year cycle. The Athenian months had names like Hekatombion and Poseidon. The extra month usually came after Poseidon and was called "second Poseidon."
Besides their regular "festival" calendar, Athenians also had a political calendar. This calendar divided the year into "prytanies." There was one for each of the "phylai," which were groups of Athenian citizens. The number of phylai changed over time. Until 307 BC, there were 10 phylai. After that, the number varied between 11 and 13. It can be hard to match dates from this political calendar to the Julian calendar.
The table of Greek Olympiads followed four-year cycles. These cycles were between the Olympic Games from July 1, 776 BC. This system continued until the end of the 4th century AD. The Babylonian Era of Nabonassar, starting on February 26, 747 BC, was used by Greeks in Alexandria. It became known in the Middle Ages through the writings of Ptolemy.
Hellenistic Period Calendars
Greek calendars became very diverse during the Hellenistic period. Each Greek state had its own traditions. The calendar of Delphi is very important for understanding these regional calendars. Many documents found there, like records of freeing slaves, are dated using both the Delphian and a regional calendar.
The Roman Republican calendar numbered years based on the sitting consuls. People used references to the year of consulship in conversations and official records. Romans from the same family often had the same first name. This sometimes made it hard to tell them apart. There were two consuls at any time. Each might hold the position more than once. This meant you needed to know a lot of history to understand the dates. The Romans had an eight-day week. The market day happened every eight days. It was called a nundinum.
Most regional Hindu calendars come from a system standardized in classical Hindu astronomy. This system was adopted through Greek influences in the last centuries BC. It was later improved by astronomers like Aryabhata and Varāhamihira during the Gupta period.
Chinese Calendars
Before the Spring and Autumn period (before 770 BC), Chinese calendars were solar calendars. In one system, the year had 10 months and a transition period. Each month was 36 days long, and transitions were 5 or 6 days. During the Warring States period (around 475–220 BC), early lunisolar calendars were set up under the Zhou Dynasty. These were known as the six ancient calendars. The months in these calendars began on the day of the new moon. A year had 12 or 13 months (moon cycles). An extra month was added at the end of the year. In Qin China, the Qin calendar was introduced. It followed the rules of an older calendar but used the month order of the Xia calendar.
Vedic and Pre-Vedic Era / Ancient India
Keeping track of time was important for Vedic religious ceremonies. Jyotisha was the Vedic-era study of tracking and predicting the movements of stars and planets. This was done to set the correct day and time for these rituals. This study developed around the end of the 2nd millennium BC. It was one of the six ancient Vedangas, or supporting sciences connected with the Vedas. The Vedas are the holy books of Hinduism.
The Brahma-siddhanta text, likely written in the 5th century AD, explains how to use the movement of planets, sun, and moon to keep time. This text also includes math formulas to predict planetary positions. It is known for using very large numbers, like 4.32 billion years for the universe's current lifetime.
Water clocks and sundials are mentioned in many ancient Hindu texts. The Jyotisha texts provide math formulas to predict the length of daylight, sunrise, and moon cycles.
The modern Hindu calendar, also called Panchanga, is a group of different lunisolar calendars used in Hinduism. They all use a similar way of keeping time. However, they differ in whether they focus more on the moon or sun cycle. They also have different month names and start their New Year at different times. The ancient Hindu calendar is similar in design to the Jewish calendar. It is different from the Gregorian calendar. The Gregorian calendar adds extra days to lunar months to match the solar year. The Hindu calendar keeps lunar months whole. Instead, it adds an extra full month every few years. This ensures that festivals and farming rituals happen in the right season.
Hindu calendars have been used in India since ancient times. Hindus in India and Nepal still use them, especially to set festival dates. Early Buddhist and Jain communities in India adopted the ancient Hindu calendar. Later, they used the Vikrami calendar and then local Buddhist calendars. Buddhist and Jain festivals are still scheduled using a lunar system within the lunisolar calendar.
Roman Empire Calendars
The old Roman year had 304 days divided into 10 months. It began with March. However, the ancient historian Livy said that the second early Roman king, Numa Pompilius, created a calendar of 12 months. The extra months Ianuarius and Februarius were supposedly invented by Numa Pompilius as temporary additions. Julius Caesar realized the system was not working well. So, he made big changes in the year of his third consulship. The New Year in 709 AUC (45 BC) began on January 1 and lasted 365 days until December 31. More changes were made under Augustus. He introduced the idea of the "leap year" in 757 AUC (AD 4). The resulting Julian calendar was used almost everywhere in Europe until 1582. Some countries used it until the 20th century.
In the first century BC, Marcus Terentius Varro introduced the Ab urbe condita (AUC) era. This system assumed Rome was founded in 753 BC. It was used in the early Middle Ages. Later, the Dionysian era became widely used during the Carolingian Renaissance.
In the Roman Empire, the AUC year could be used alongside the consular year. For example, the consulship of Quintus Fufius Calenus and Publius Vatinius was 707 AUC (47 BC). The third consulship of Gaius Julius Caesar, with Marcus Aemilius Lepidus, was 708 AUC (46 BC). The fourth consulship of Gaius Julius Caesar was 709 AUC (45 BC).
The seven-day week has roots in the ancient Near East. However, the "planetary week" we still use today began in the Roman Empire.
Calendars in the Middle Ages
Christian Europe Calendars
The oldest calendar of saints for the Church of Rome was made in the mid-4th century. It included both non-Christian and Christian festivals. The oldest surviving early Christian calendar is the Calendar of Filocalus, made in AD 354. A larger list of saints was put together by Jerome in the early 5th century. The Anno Domini (AD) era was introduced in the 6th century. Early medieval calendars used Jerome's system for numbering the years of the Metonic cycle. These were later called Golden Numbers.
In the 8th century, the Anglo-Saxon historian Bede the Venerable used a Latin term. It meant "the time before the Lord's true incarnation." This is like the English "before Christ" (BC). According to the Catholic Encyclopedia, even Popes continued to date documents using their own reign years. The use of AD slowly became common in Europe from the 11th to the 14th centuries. In 1422, Portugal was the last Western European country to adopt the Anno Domini system.
The Icelandic calendar was introduced in the 10th century. Old Germanic calendars used lunar months. But the new Icelandic calendar used a purely solar count. A year had a fixed number of weeks (52 weeks or 364 days). This meant they added "leap weeks" instead of leap days, like in the Julian calendar.
In 1267, the medieval scientist Roger Bacon stated the times of full moons. He gave them as hours, minutes, seconds, thirds, and fourths after noon on specific dates. While a "third" for 1/60 of a second is still used in some languages, the modern second is divided into smaller decimal parts.
Other calendar eras were used in Christian Europe besides Anno Domini. In Spain, the "Era of the Caesars" started from Octavian's conquest of Spain in 39 BC. The Visigoths adopted it. It was used in Catalonia until 1180, Castile until 1382, and Portugal until 1415.
For tracking history, the AD system had a problem. Dates had to be counted backward or forward depending on if they were BC or AD. For both Christians and Jews, a main historical date was the Year of Creation, or Annus Mundi. The Eastern Orthodox Church set the date of Creation at 5509 BC. This was the basis of the church calendar in the Greek and Russian Orthodox world until modern times. The Coptic Church set it at 5500 BC. Later, the Church of England, under Archbishop Ussher in 1650, chose 4004 BC.
Islamic Calendar
The Islamic calendar is based on a rule against adding extra months. This rule was set by Muhammad. In Islamic tradition, it dates to a sermon on 9 Dhu al-Hijjah AH 10 (March 6, 632 AD). This resulted in a lunar calendar that shifts compared to the seasons of the solar year.
During the Mughal rule, land taxes were collected from Bengali people using the Islamic Hijri calendar. This was a lunar calendar. Its new year did not match the solar farming cycles. Some sources say Mughal Emperor Akbar asked his astronomer Fathullah Shirazi to create a new calendar. This calendar combined the lunar Islamic calendar and solar Hindu calendar. It was called Fasholi shan (harvest calendar). According to Amartya Sen, Akbar's official calendar "Tarikh-ilahi" (with a zero year of 1556 AD) was a mix of Hindu and Islamic calendars. It was not used much outside Akbar's court. After his death, it was abandoned. However, Sen adds that parts of the "Tarikh-ilahi" survive in the Bengali calendar. Some historians believe the Bengali calendar came from the 7th-century Hindu king Shashanka.
Other Medieval Calendars
The ancient Taichu calendar of China was improved in the medieval period. The Dàmíng Calendar, created by Zu Chongzhi, introduced the equinoxes. The use of a syzygy (alignment of celestial bodies) to find the lunar month was first described in the Tang dynasty Wùyín Yuán Calendar.
The Yuan dynasty (13th/14th century) Shòushí calendar used advanced math to find the length of the tropical year. This calendar had a 365.2425-day year, which is the same as the Gregorian calendar.
Sub-Saharan African Calendars
Ethiopian Calendar
The Ge'ez or Ethiopian Calendar comes from the Ethiopian Empire. It is the church year for Ethiopian and Eritrean Christians. It is very similar to the Coptic Christian calendar.
Nigerian Calendars
The Igbo calendar is the traditional calendar of the Igbo from Nigeria. The calendar has 13 months in a year, 7 weeks in a month, and 4 Igbo market days in a week. It also has an extra day at the end of the year. The Yoruba calendar is used by the Yoruba of southwestern Nigeria and southern Benin. The year starts on the last new moon of May or the first new moon of June in the Gregorian calendar. The new year matches the Ifá festival. The traditional Yoruba week has four days. These days are dedicated to the Orisa (gods).
Ghana/West African Calendars
The Akan Calendar was created by the Akan (a group from West Africa). They used a traditional system of timekeeping based on a six-day week. The Gregorian seven-day week is also known. Combining these two systems led to periods of 40 days.
Xhosa Calendar
The traditional isiXhosa names for months come from stars, plants, and flowers. They also come from seasonal changes in Southern Africa.
The Xhosa year traditionally begins in June and ends in May. This is when Canopus, a very bright star, signals the time for harvesting.
Mesoamerican Calendars
Among all ancient calendar systems, the Maya and other Mesoamerican systems are the most complex. The Maya calendar had two main years. One was the 260-day Sacred Round, or tzolkin. The other was the 365-day Vague Year, or haab.
The Sacred Round of 260 days had two smaller cycles. These were numbers 1 through 13, combined with 20 different day names. The Sacred Round was used for important activities. These included naming people, predicting the future, and choosing good dates for battles or weddings.
The two cycles of 13 and 20 worked together and repeated. For example, the cycle would start with 1 Imix, then 2 Ik, then 3 Akbal, and so on. When the number 13 was reached, the number cycle restarted. So, 13 Ben would be followed by 1 Ix. The cycle ended after 260 days, with the last day being 13 Ahau.
The Vague Year of 365 days is similar to the modern Gregorian calendar. It had 18 months of 20 days each. There was also an unlucky five-day period at the end. The Vague Year was mainly about seasons and farming. It was based on the solar cycle. The 18 Maya months had names like Pop, Uo, and Zip. The unlucky five-day period was called Uayeb. It was seen as a time of danger and bad luck.
The Vague Year began with the month of Pop. A Maya 20-day month always started with the "seating" of the month. Then came days 1 to 19. After that, it was the "seating" of the next month, and so on. This showed the Maya idea that each month influenced the next. The Maya new year would start with 1 Pop, then 2 Pop, all the way to 19 Pop. Then came the seating of the month of Uo (written as 0 Uo), then 1 Uo, and so on. These two cycles (Sacred Round and Vague Year) matched up every 52 years. This 52-year period was called a "bundle." It was like a century in our modern calendar.
Modern Calendars
The Gregorian calendar is now used worldwide for everyday purposes. However, various medieval or ancient calendars are still used in different regions for religious or social reasons. These include the Julian calendar, the Hebrew calendar, the Islamic calendar, various Hindu calendars, and the Zoroastrian calendar.
There are also several modern calendars that are used in limited ways. Some were created for new religious groups. Others are updated versions of older religious calendars. Some were introduced by regional or nationalist movements.
- Javanese calendar (1633)
- Jōkyō calendar (1685)
- French Republican calendar (1793)
- Baháʼí calendar (1873)
- Solar Hijri calendar (1925)
- Pataphysical calendar (1949)
- Indian national calendar (1957)
- Discordian calendar (1963)
- Juche calendar (1997)
See also
- Names of the days of the week
- History of timekeeping devices
