Introduction

This calendar represents an effort to simulate every calendrical system in use in Western Civilisation for almost 3000 years, and to synchronise those calendars with the modern form of dating.

On this page the Roman Calendar begins in 900 BCE with a lunar calendar which recorded just ten months from March to December, without assigning dates during the winter time. From the year of the traditional foundation of Rome, 753 BCE, the calendar switches from purely lunar to the calendar of Romulus, with 31 and 30-day months over exactly 38 market days. January and February were added as months around the year 700 BCE, and this calendar shows them from 693 BCE.

In 45 BCE Julius Caesar reformed the calendar to create the Julian calendar, named after him. This dominated the world for more than 1600 years, before a more accurate calendar was devised, the Gregorian, which we use to this day.

Select "Gregorian Date" to show the seasonal adjusted date as it would be today. This will demonstrate the shift in the seasons between the creation of the Julian calendar and the adoption of the Gregorian. For the lunar calendar period (900-694 BCE) it will give roughly accurate dates derived from the new moon that begins each month. For all years prior to 900 BCE the calendar reverts to Julian dates, in common with modern astronomical and historical practice.

The "Date of Easter" option shows, from AD 532 onward, the dates of Good Friday and Easter Sunday in a normal calendar.

As this project has grown and evolved into a general chronological tool, for each date its Mayan Long Count number and its Julian Day Number as used by astronomers, can be displayed.

For the years 753 BCE to 799 CE, the year in the title bar is in the Roman system, counting from the founding of Rome and labelled A.U.C. (ab urbe condita, which means "since the founding of the City"). (This option can be turned off.) Anno Domini (A.D.) numbering begins from 800, the year Charlemagne was crowned Holy Roman Emperor. The Carolingians were the first to date treaties, contracts and other documents using the Anno Domini system.

Months of the Year

The Roman months are Ianuarius, Februarius, Martius, Aprilis, Maius, Iunius, Iulius, Augustus, September [sic], October, November, December *. These gave the month names in the majority of European languages. September to December are named after their numerical position in the calendar (counting from March, the original first month). In Latin, seven, eight, nine and ten are septem, octo, novem and decem. Prior to Julius Caesar's death, the fifth and sixth months were originally named Quintilis (or Quinctilis) and Sextilis. Quintilis was renamed Iulius (now July) in 44 BCE in honour of Julius Caesar, following his assassination. Sextilis became Augustus (August) in 8 BCE, after Emperor Augustus, the then reigning Emperor.

The Roman System of Dates

The Romans didn't number the days of the month sequentially as we do today. They counted in descending order towards three special days common to every month, the Kalends, the Nones and the Ides. The Kalends was the first day of the month. The Ides, the mid-month public holiday, was on the 13th day of most months, but the 15th day of the four long (31-day) months: March, May, July and October. The Nones was always eight days before the Ides (and so named because Romans thought of it as the ninth day to the Ides). The Nones was therefore either four or six days after the Kalends.

Each date was called by the number of days to the next special day, plus one. For example, the 1st of January is Kalendis Ianuarius. The next significant day is the Nones, which is the 5th. Although the 2nd is three days before the 5th, counting inclusively it is four days - 2nd, 3rd, 4th, 5th. So 2nd January became "4th day to the Nones of January", or in Latin a.d. IV Nonas Ianuarius The abbreviation 'a.d.' stands for ante diem, Latin for "day before".

Another example: 10th July, 5 days before the Ides on the 15th, becomes a.d. VI Eidus Iulius. Then the 11th is a.d. V Eid. Iul., the 12th a.d. IV Eid. Iul. and so on.

After the Ides the next counting day is the Kalends of the following month. This means that, paradoxically, more than half of the days within a month have the name of the upcoming month in them, e.g. 23rd September (Julian) was a.d. IX Kal. Oct, the 9th day to the Kalends of October.

The "Eve" of each of the Kalends, the Nones and the Ides, which might normally have been referred to as a.d. II, was instead called Pridie (pre-day), so 12 June would be Pridie Eidus Iunius and 31 December is Pridie Kalendas Ianuarius.

Market Day

In Roman times every eighth day was the market day. The market day was called the nundinum, derived from the Latin for "nine days", because, even though they are only eight days apart, if you count a market day as day one then the next market day is day nine. Some feasts had to be moved if they coincided with the nundinum, just as we take extra holidays when Christmas falls on Saturday or Sunday.

Although the Romans did not use what we would regard as regular weekdays, they marked each day on their Fasti in sequences of eight using the letters A to H. This was not like naming the days of the week - a Roman wouldn't say "I'll see you on D of next week" - but simply acted as a ready reckoner to see when the next nundine would be. On a publicly displayed Fasti, the letter sequence began with 'A' on the Kalends of January. If the first nundinum of the year was two days later, marked 'C', that meant all market days for that year would fall on the 'C' days. In that way the Fasti acted as a perpetual calendar. The Kalends of January 40 BCE should have been a market day but was postponed to the next day. Because of this, the last day of 41 BCE is considered a nundinum, and every eighth day before and after, throughout history, is marked in red.

Character of the Day

Every day had a special character, designated by one or two inital letters. The meanings are indicated by the following table:

History

Calendar of Romulus

The first known calendar used by the Romans was what became known as the Calendar of Romulus, after the legendary founder and first king of Rome. The Romulan calendar originated from a true lunar calendar, and it named ten months, from March (the month of the spring equinox), to December (the month of the winter solstice and Saturnalia). There were no months between the end of December and the beginning of March, just a general "winter time" when little business was transacted and dates were not recorded. The new year would begin when the new moon heralded the month of Spring Equinox. March has been the month of the Spring Equinox to this day.

During the ten-month calendar, four months had 31 days and the rest 30 days, for a total of 304 days, or 38 nundines (market periods). The moon phases at the Kalends and Ides are shown (roughly new moon and full moon respectively).

Numa's reform and the Republic era

King Numa, the second King of Rome, is credited with reforming the calendar. Two new months, Ianuarius and Februarius, were added. This remained the calendar system used throughout the era of the Roman Republic.

The reform also modified the original months so that none of the months other than February had an even number of days (which the Romans regarded as unlucky). Four months had 31 days and the rest had 29. February had 28 days every year.

The calendar of Numa alternated 12 month years (355 days) with 13 month years (377 or 378 days). The extra month was known as Intercalaris or Mercedonius, a 22-day month inserted after the 23rd or 24th day of February. (The one extant Fasti of the period showed Intercalaris as a 27-day separate month, however, and this page does the same. The citizenry were given to understand that the last 5 days of Intercalaris were to be thought of as the last 5 days of February, and they had the same festivals.)

The reformed calendar had a cycle of 1465 days over four years, which is four days too long for the Earth's circa 365.25 day orbit. To keep the calendar synchronised with the tropical year, this program uses a 24-year cycle. With 4 days extra every 4 years, after 24 years the calendar is 24 days out, or the length of February in an intercalary year. Therefore, in the 24th and final year of the cycle, the intercalary month is omitted, resetting the calendar so that Kalendas Ianuarius falls on January 1st. The 24-year cycle was created independently for this web site program, and only afterwards it was discovered that this system was very close to a genuine 24-year cycle with an omitted intercalary month, which was described by Macrobius in his classic work, the Saturnalia.

The Julian Calendar

For many years in the 1st Century BCE, intercalary years had been neglected, putting the calendar badly out of synchronisation with the seasons. By 46 BCE New Year's Day occurred in what in modern terms would be early October. To rectify this problem, Julius Caesar realigned the calendar by making 46 BCE an intercalary year, and he also added two extra months between November and December, so that 46 BCE was 15 months - 445 days - long. Then he decreed a new solar calendar, which began in 45 BCE. This was the origin of the 365/6-day calendar we use today, with the same number of days in each of the months as we have now, as well as the four-yearly Leap day cycle.

Julius Caesar was to enjoy the use of his new calendar for less than 15 months before being assassinated, famously on the Ides of March (Eidus Martius), in 44 BCE; but the calendar has lasted for more than two millennia since, and looks likely to stay in use for another two.

This program simulates a lack of intercalation for the years 55 to 47 BC, and the "year of confusion" of 46 BCE (put -45 in the year input, or click here, to see the 15 month year). Also, note that for the first 40 years, the pontiffs mistakenly made every third year a leap year, instead of every fourth year. This had to be rectified by Emperor Augustus, who proclaimed there would be no leap years at all until the calendar matched the Alexandrian version, which had been Julius's original intention. Leap years resumed in AD 8, and every year divisible by four (except three times since the Gregorian reform, see below) has been a leap year ever since.

Calendar slippage and the Gregorian Reform

Because the Julian year of 365.25 days was slightly longer than the actual tropical year of 365.24219 days, the Julian calendar lost its accuracy over time. Over the period of one and a half millennia, it became noticeable that the dates no longer matched the seasons.

The maintenance of the calendar dates since the Roman era was the province of the Roman Catholic church. They were concerned that the actual (ie astronomical) Vernal Equinox fell at least 10 days before the date set for it, the 21st of March, which was part of the calculation of the date of Easter. Pope Gregory XIII decreed a new design of calendar, and the extra accumulated days were skipped in one go, dropping 10 days from October 1582.

At this time, not many years after the Protestant Reformation, acceptance of the new calendar was not universal. Most Protestant countries in Europe stayed on the Julian calendar until the early 18th century. In Great Britain and its colonies, including America, the Julian calendar was not replaced until as late as 1752, when September 2nd was followed by the 14th. Countries which followed Orthodox Catholicism (among them Greece, the Russian Empire and Ethiopia) were even more recalcitrant, not relinquishing the Julian calendar until the 20th Century.

The Calendar Today

The Gregorian calendar is the one in worldwide use today. It differs from the Julian calendar only in that it omits 3 leap years every 400 years. The 365.25 day per year calendar is too long, by three quarters of one day per century. The Gregorian calendar rectifies the error by omitting leap days in Century years - years divisible by 100 - unless they are also divisible by 400. This slips the calendar back 0.0075 days per year. Subtracting 0.0075 from 365.25 gives 365.2425, which differs from the accurate length of the tropical year by 0.0003 of a day. Further adjustments, (3 days per 10 000 years), will have to wait for some future global agreement.