An era is a commonly used word for long period of time. When used in science, for example geology, eras denote clearly defined periods of time of arbitrary but well defined length, such as for example the Mesozoic era from 252 Ma–66 Ma, delimited by a start event and an end event. When used in social history, eras may for example denote a period of some monarch's reign. In colloquial language, eras denote longer spans of time, before and after which the practices or fashions change to a significant degree.


In chronology
Chronology is the science of arranging events in their order of occurrence in time, such as the use of a timeline or sequence of events. It is also "the determination of the actual temporal sequence of past events".Chronology is part of periodization...

, an era is the highest level for the organization of the measurement of time
Time is a part of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify rates of change such as the motions of objects....

. A calendar era
Calendar era
A calendar era is the year numbering system used by a calendar. For example, the Gregorian calendar numbers its years in the Western Christian era . The instant, date, or year from which time is marked is called the epoch of the era...

indicates a span of many years which are numbered beginning at a specific reference date (epoch)
Epoch (reference date)
In the fields of chronology and periodization, an epoch is an instance in time chosen as the origin of a particular era. The "epoch" then serves as a reference point from which time is measured...

, which often marks the origin of a political state or cosmology
Cosmology is the discipline that deals with the nature of the Universe as a whole. Cosmologists seek to understand the origin, evolution, structure, and ultimate fate of the Universe at large, as well as the natural laws that keep it in order...

, dynasty, ruler, the birth of a leader, or another significant historical or mythological event; it is generally called after its focus accordingly as in Victorian era
Victorian era
The Victorian era of British history was the period of Queen Victoria's reign from 20 June 1837 until her death on 22 January 1901. It was a long period of peace, prosperity, refined sensibilities and national self-confidence...


Regnal eras

The word era also denotes the units used under a different, more arbitrary system where time is not represented as an endless continuum with a single reference year, but each unit starts counting from one again, as if time starts again. The use of regnal year
Regnal year
A regnal year is a year of the reign of a sovereign, from the Latin regnum meaning kingdom, rule.The oldest dating systems were in regnal years, and considered the date as an ordinal, not a cardinal number. For example, a monarch could have a first year of rule, a second year of rule, a third, and...

s is a rather impractical system, and a challenge for historians if a single piece of the historical chronology is missing, and often reflects the preponderance in public life of an absolute ruler in many ancient cultures. Such traditions sometimes outlive the political power of the throne, and may even be based on mythological events or rulers who may not have existed (for example Rome numbering from the rule of Romulus and Regulus). In a manner of speaking the use of the supposed date of the birth of Christ as a base year is a form of a Regnal era.

In East Asia
East Asia
East Asia or Eastern Asia is a subregion of Asia that can be defined in either geographical or cultural terms...

, each emperor's reign may be subdivided into several reign periods, each being treated as a new era. The name of each was a motto or slogan chosen by the emperor. Different East Asian countries utilized slightly different systems, notably:
  • Chinese eras
    Chinese era name
    A Chinese era name is the regnal year, reign period, or regnal title used when traditionally numbering years in an emperor's reign and naming certain Chinese rulers . Some emperors have several era names, one after another, where each beginning of a new era resets the numbering of the year back...

  • Japanese eras
    Japanese era name
    The Japanese era calendar scheme is a common calendar scheme used in Japan, which identifies a year by the combination of the and the year number within the era...

  • Korean eras
    Korean era name
    Korean era names were used during the period of Silla, Goguryeo, Balhae, Taebong, Goryeo, Joseon, and the Korean Empire. Dangun-giwon, the era name originating from the foundation of Gojoseon is also widely used in Korea as an indication of long civilisation of Korea.-Goguryeo:#Yeongnak Korean era...

  • Vietnamese eras
    Vietnamese era name

A similar practice survived in the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

 until quite recently, but only for formal official writings: in daily life the ordinary year A.D. has been used for a long time, but Acts of Parliament were dated according to the years of the reign of the current Monarch, so that "61 & 62 Vict c. 37" refers to the Local Government (Ireland) Act 1898
Local Government (Ireland) Act 1898
The Local Government Act 1898 was an Act of the Parliament of the United Kingdom that established a system of local government in Ireland similar to that already created for England, Wales and Scotland by legislation in 1888 and 1889...

 passed in the session of Parliament
Parliament of the United Kingdom
The Parliament of the United Kingdom of Great Britain and Northern Ireland is the supreme legislative body in the United Kingdom, British Crown dependencies and British overseas territories, located in London...

 in the 61st/62nd year of the reign of Queen Victoria
Victoria of the United Kingdom
Victoria was the monarch of the United Kingdom of Great Britain and Ireland from 20 June 1837 until her death. From 1 May 1876, she used the additional title of Empress of India....


Geological era

In natural science, there is need for another time perspective, independent from human activity, and indeed spanning a far longer period (mainly prehistoric), where geologic era refers to well-defined time spans. The next-larger division of geologic time is the eon. The Phanerozoic
The Phanerozoic Eon is the current eon in the geologic timescale, and the one during which abundant animal life has existed. It covers roughly 542 million years and goes back to the time when diverse hard-shelled animals first appeared...

 Eon, is subdivided into eras. There are currently three eras defined in the Phanerozoic; the following table lists them from youngest to oldest (BP is an abbreviation for "before present").
Era Beginning (millions of years BP) End (millions of years BP)
The Cenozoic era is the current and most recent of the three Phanerozoic geological eras and covers the period from 65.5 mya to the present. The era began in the wake of the Cretaceous–Tertiary extinction event at the end of the Cretaceous that saw the demise of the last non-avian dinosaurs and...

70 0
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...

225 70
The Paleozoic era is the earliest of three geologic eras of the Phanerozoic eon, spanning from roughly...

570 225

Cosmological era

In astronomy the periods are even longer, to cover the entire existence of the universe (in the order of 13.7 billion years), but usually just denoted in numerical units, as there is no significant link to any earthly reality, our planet being astronomically insignificant (except as the only known observation point).

Religious era

The term Christian era refers to Anno Domini
Anno Domini
and Before Christ are designations used to label or number years used with the Julian and Gregorian calendars....

, the time when Jesus was born and Christianity began, while the expressions Jewish era and Islamic era indicates the time since those religions began.

Colloquial "eras"

In common speech and various contexts, the term era is also used, by extension, for any (as a rule relatively long) period in history with a name, often relating to common characteristic(s), even if this is not the normal way to organize time. The most relevant type are politic periods, for example: the Roman era, the Elizabethan era
Elizabethan era
The Elizabethan era was the epoch in English history of Queen Elizabeth I's reign . Historians often depict it as the golden age in English history...

, the Victorian era
Victorian era
The Victorian era of British history was the period of Queen Victoria's reign from 20 June 1837 until her death on 22 January 1901. It was a long period of peace, prosperity, refined sensibilities and national self-confidence...

 (dynastic criteria, only formally correct within the British realm/empire/Commonwealth) and the Soviet era, or comparable literary notions like the Biblical era.

The word era is also popularly used to denote the passing of often shorter periods that are only defined in terms of a specific discipline of sphere of life, such as the prominence of an artistic style, or more specifically in music
Music is an art form whose medium is sound and silence. Its common elements are pitch , rhythm , dynamics, and the sonic qualities of timbre and texture...

, see musical eras, described in History of music
History of music
Music is found in every known culture, past and present, varying wildly between times and places. Around 50,000 years ago, early modern humans began to disperse from Africa, reaching all the habitable continents...

, such as the Big Band era
Big band
A big band is a type of musical ensemble associated with jazz and the Swing Era typically consisting of rhythm, brass, and woodwind instruments totaling approximately twelve to twenty-five musicians...

, Disco era. An event such as the death of Frank Sinatra
Frank Sinatra
Francis Albert "Frank" Sinatra was an American singer and actor.Beginning his musical career in the swing era with Harry James and Tommy Dorsey, Sinatra became an unprecedentedly successful solo artist in the early to mid-1940s, after being signed to Columbia Records in 1943. Being the idol of the...

 is poetically called the end of an era.


The word has been in use in English since 1615, and is derived from Late Latin
Late Latin
Late Latin is the scholarly name for the written Latin of Late Antiquity. The English dictionary definition of Late Latin dates this period from the 3rd to the 6th centuries AD extending in Spain to the 7th. This somewhat ambiguously defined period fits between Classical Latin and Medieval Latin...

 aera "an era or epoch from which time is reckoned," probably identical to Latin æra "counters used for calculation," plural of æs "brass, money".

The Latin word use in chronology seems to have begun in 5th century Visigothic Spain, where it appears in the History of Isidore of Seville
Isidore of Seville
Saint Isidore of Seville served as Archbishop of Seville for more than three decades and is considered, as the historian Montalembert put it in an oft-quoted phrase, "le dernier savant du monde ancien"...

, and in later texts. The Spanish era
Spanish era
The Spanish era, Hispanic era or Caesar era refers to the dating system used in Hispania until the 14th century, when the Anno Domini system was adopted. It began with year one in what is 38 BC, probably the date of a new tax imposed by the Roman Republic on the subdued population of Iberia....

 is calculated from 38 BC, perhaps because of a tax (cfr. indiction
An indiction is any of the years in a 15-year cycle used to date medieval documents throughout Europe, both East and West. Each year of a cycle was numbered: first indiction, second indiction, etc...

) levied in that year, or due to a miscalculation of the Battle of Actium
Battle of Actium
The Battle of Actium was the decisive confrontation of the Final War of the Roman Republic. It was fought between the forces of Octavian and the combined forces of Mark Antony and Cleopatra VII. The battle took place on 2 September 31 BC, on the Ionian Sea near the city of Actium, at the Roman...

, which occurred in 31 BC.

Like epoch, "era" in English originally meant "the starting point of an age"; the meaning "system of chronological notation" is c.1646; that of "historical period" is 1741.
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