Chinese era names, also known asreign mottos, were titles used by variousChinese dynasties and regimes inImperial China for the purpose ofyear identification and numbering. The first monarch to adopt era names was theEmperor Wu of Han in 140 BCE,^[1][2] and this system remained the official method of year identification and numbering until the establishment of theRepublic of China in 1912 CE, when the era name system was superseded by theRepublic of China calendar. Other polities in theSinosphere—Korea,Vietnam andJapan—also adopted the concept of era name as a result of Chinese politico-cultural influence.^[2][3][4]

Chinese era names were titles adopted for the purpose of identifying and numbering years in Imperial China. Era names originated as mottos or slogans chosen by the reigningmonarch and usually reflected the political, economic and/or social landscapes at the time. For instance, the first era name proclaimed by theEmperor Wu of Han,Jianyuan (建元; lit. "establishing the origin"), was reflective of its status as the first era name. Similarly, the era nameJianzhongjingguo (建中靖國; lit. "establishing a moderate and peaceful country") used by theEmperor Huizong of Song was indicative of Huizong's idealism towards moderating the rivalry among the conservative and progressive factions regarding political and social reforms.

The process of declaring an era name was referred to in traditional Chinese historical texts asjiànyuán (建元). Proclaiming a new era name to replace an existing era name was known asgǎiyuán (改元; lit. "change the origin"). Instituting a new era name would reset the numbering of the year back to year one, known asyuán nián (元年; lit. "year of origin"). On thefirst day of theChinese calendar, the numbering of the year would increase by one. To name a year using an era name only requires counting years from the first year of the era. For example, 609 CE was the fifth year ofDaye (大業; lit. "great endeavour"), as the era began in 605 CE; traditional Chinese sources would therefore refer to 609 CE asDàyè wǔ nián (大業五年).

The numbering of the year would still increase on the first day of the Chinese calendar each year, regardless of the month in which the era name was adopted. For example, as theEmperor Daizong of Tang replaced the era nameYongtai (永泰; lit. "perpetual peace") withDali (大曆; lit. "great era") in the eleventh month of the Chinese calendar in 766 CE, the first year ofDali thus only consisted of the last two months of that particular year; the second year ofDali began on the first day of the Chinese calendar the following year, just two months after its initiation.

When a new monarch ascended to the throne, he could either declare a new era immediately or inherit the usage of the existing era name from his predecessor. For example, the era nameWutai (武泰; lit. "exalted martial") of theEmperor Xiaoming of Northern Wei was immediately replaced withJianyi (建義; lit. "establishing justice") when theEmperor Xiaozhuang of Northern Wei took the throne. On the other hand, the era nameTianxian (天顯; lit. "heavenly intent") was originally proclaimed by theEmperor Taizu of Liao but its usage was continued by theEmperor Taizong of Liao upon assuming the throne.

There were numerous era names that saw repeated use throughout Chinese history. For instance, the era nameTaiping (太平; lit. "great peace") was used on at least ten occasions in China. In such cases, Chinese sources would often affix the name of the dynasty or the ruler before the era name for the purpose of disambiguation. For example, when referencing the year 410 CE, Chinese sources could either render it asBěi Yān Tàipíng èr nián (北燕太平二年; lit. "second year ofTaiping of theNorthern Yan") orBěi Yān Wéngchéng Dì Tàipíng èr nián (北燕文成帝太平二年; lit. "second year ofTaiping of theEmperor Wencheng of Northern Yan).

Most Chinese era names consisted of twoChinese characters, even though era names with three, four and six characters also existed.Shijianguo (始建國; lit. "the beginning of establishing a country") of theXin dynasty,Tiancewansui (天冊萬歲; lit. "Heaven-conferred longevity") of theWu Zhou, andTiancilishengguoqing (天賜禮盛國慶; lit. "Heaven-bestowed ritualistic richness, nationally celebrated") of theWestern Xia are examples of Chinese era names that bore more than two characters.

Era names were symbols of political orthodoxy and legitimacy. Hence, most Chinese monarchs would proclaim a new era upon the founding of a new dynasty. Rebel leaders who sought to establish independence and legitimacy also declared their own era names. Often, vassal states andtributary states of Imperial China would officially adopt the era name of the reigning Chinese monarch as a sign of subordination—a practice known asfèng zhēng shuò (奉正朔; lit. "following the first month of the year and the first day of the month").^[5][6] For example, Korean regimes such asSilla,Goryeo, andJoseon at various times formally adopted the era names of theTang, Wu Zhou,Later Liang,Later Tang,Later Jin,Later Han,Later Zhou,Northern Song,Liao,Jin,Yuan,Northern Yuan,Ming, andQing dynasties of China for both domestic and diplomatic purposes.

TheEmperor Wu of Han is conventionally regarded as the first ruler to declare an era name.^[1][2] Prior to the introduction of the first era name in 140 BCE, Chinese monarchs utilized theQianyuan (前元),Zhongyuan (中元) andHouyuan (後元) systems to identify and number years.

Prior to theMing dynasty, it was common for Chinese sovereigns to change the era name during their reigns, resulting in the use of more than one era name for one ruler. For instance,Emperor Xuan of Han used a total of seven era names during his reign.

TheHongwu Emperor started the tradition of having only one era name for one monarch—known as theyí shì yì yuán zhì (一世一元制; lit. "one-era-name-for-a-reign system").^[7] Thus, modern historians would frequently refer to monarchs of the Ming andQing dynasties by their respective era name. Notable exceptions to this "one-era-name" tradition includedZhu Qizhen who proclaimed two era names for his two separate reigns,Aisin Gioro Hong Taiji who used two era names to reflect his position as khan of theLater Jin and later as emperor of the Qing dynasty, as well asAisin Gioro Puyi who adopted three era names in his capacity as emperor of the Qing dynasty and subsequently as ruler ofManchukuo.

With the establishment of theRepublic of China in 1912 CE, the Chinese era name system was superseded by theRepublic of China calendar which remains in official use inTaiwan, Penghu, Kinmen, and Matsu Islands. The Republic of China calendar, while not an era name,^{[citation needed][dubious –discuss]} is based on the era name system of Imperial China. Numerous attempts to reinstate monarchical rule in China had resulted in the declaration of additional era names after the founding of the Republic, but these regimes and their associated era names were short-lived.

In 1949, thePeople's Republic of China was founded and the era was changed to theCommon Era, for both internal and external affairs inmainland China. This notation was extended toHong Kong in 1997 andMacau in 1999 (de facto extended in 1966) through Annex III ofHong Kong Basic Law andMacau Basic Law, thus eliminating the ROC calendar in these areas.

The concept of era name also saw its adoption by neighboringKorea andVietnam since the middle of the 6th century CE, and byJapan since the middle of the 7th century CE.^[2][3][4] Notably, Japan still officially retains the use of era names today.^[4]

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While the era system is a more traditional system of dating that preserves Chinese and Japanese culture, it presents a problem for the more globalized Asian society and for everyday life.

For example, even though within the nation people will know what era they are in, it is relatively meaningless for other nations. In addition, while the Republic of China (ROC) and Japan only recognize documents dated in the Era System, their treaties with other countries are in theDionysian Era (AD) system. In modern times, only Republic of China and Japan still continue to use the ancient Chinese era naming system.

Even in the domestic arena, the era system can present difficult dilemmas. For example, in Japan, it is difficult to keep track of the age of people who were born in the previous era. Also, while the ROC and Japan both continue to use the ancient Chinese era system, since they have partially adopted theGregorian calendar for non-governmental use, it is more difficult to track down dates that fall on February 29leap year in the Western calendar.

Furthermore, in Japan, in theory it is difficult to mention future dates since it is sometimes hard to tell whether the current emperor will live long enough for its citizens to use that era name. However, in practice, documents like driver's licenses and 50-year leases use era dates without regard to this problem.

On the other hand, others^[who?] suggest that the AD system has too much Christian connotation behind it and it is a form ofcultural imperialism when an essentially European system of dating is forced upon other civilizations with their own long-used and equally legitimate dating systems. However, with globalization, the AD system is becoming more acceptable in Japan and the ROC.

Modern history researchers do not care about era names except for supporting other arguments, such as figuring out the biases and attitudes of a particular historian;^{[citation needed]} however, era names are useful for dating events that were unique in Chinese history. MostChinese dictionaries have a comprehensive list of era names, while booklets of more detailed and often searchable lists can be found inlibraries.

• Comparative historical timelines and era names of China, Japan and Korea (in Japanese)

• Chinese imperial eras
• Calendar eras
• Historical eras
• Chinese calendars
• Chinese names

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