A Chinese era name (simplified Chinese: 年号; traditional Chinese: 年號; pinyin: niánhào)

How the Era System worked

Emperor Wu of Han (Han Wudi) was conventionally regarded as the first emperor to declare an era name; however he was only the first to use an era name in every year of his reign. His grandfather and father also employed era names, though not continuously. Han Wudi changed period titles every five years or so, going through a total of eleven reigning slogans during his reign from 140 BC to 87 BC.

Each era name has a literary meaning. For instance, the first era name of Han Wudi was Jianyuan (建元 in pinyin: jiàn yuán), literally meaning "establishing the First". Era names also reflected characteristics of political and other landscapes at the time. Jianzhongjingguo (建中靖國 jiàn zhōng jìng guó), the first era name of Emperor Huizong of Song China, means "establishing a happy medium and cleansing the country", reflecting his idealism towards moderating the rivalry among the conservative and progressive parties on political and social reformation. The very first era name of the Qing was significant because it means "(the Manchus possess)the Mandate of Heaven".

The process of era name declaration was referred to in traditional Chinese history texts as jianyuan. Declaring a new era name to replace an old one during an emperor's reign was referred to as gaiyuan (改元 gǎi yuán), literally meaning "change the First".

To name a year using an era name only requires counting years from the first year of the era. For example 138 BC was the third year of Jianyuan (建元), since 140 BC was the first year. When more than one monarch used the same motto, the name of the specific monarch or dynasty has to be mentioned. For instance both Han Wudi and Jin Kangdi picked Jianyuan as their motto. Thus 344 AD was the second year of Jianyuan of the Jin Dynasty (or of Jin Kangdi) whereas 139 BC was the second year of Jianyuan of the Han Dynasty (or of Han Wudi). In traditional literature, one can therefore find references like "the first month of the thirteenth year of Jianyuan" (建元十三年元月).

Almost all era names have exactly two characters. Notable exceptions are from the non-Han Chinese Western Xia Dynasty (1032 - 1227). Of the 33 Western Xia era names, seven have more than three characters. For example,

Tiancilishengguoqing (天賜禮盛國慶 tiān cì lǐ shèng guó qìng) (1070) "Heaven-given ritualistic richness, nationally celebrated"

Tianshoulifayanzuo (天授禮法延祚 tiān shòu lǐ fǎ yán zuò) (1038) "Heaven-instructed rituals and laws, perpetually blessed"

Before the Ming dynasty, an emperor often changed his era name as often as he liked. The numbering of the year still increases on the first day of the Chinese calendar each year, regardless of the month in which the era name change took place. For example, Emperor Xuanzong of Tang change his era name, Xiantian (先天, pinyin: xiān tiān) to Kaiyuan (开元, pinyin: kāi yuán) in the twelfth (i. e. last) month of the Chinese calendar. The second year of Kaiyuan (开元二年) began on the first day of the next month (i. e. Chinese New Years Day; January); this made the first year of Kaiyuan (开元元年) consist of only the last few days in the twelfth month following the name change.

Ming and Qing emperors generally used only one era name during their reign, and it is customary to refer to Ming and Qing emperors by their era names. When an emperor died, his successor would adopt a new era name but the numbering of the new era name would only begin on the next New Years Day. For example, when the Kangxi Emperor of Qing acceded the throne in 1661, it was a few days after Chinese New Year's Day, so the Shunzhi era continued for the rest of the year, and the first year of Kangxi (康熙元年) would only start on Chinese New Year's Day the following year, in 1662. Exceptions to this are the Taichang Emperor of Ming (being dead after reigning for only one month), Zhengtong Emperor of Ming and Hung Taiji of Qing (both used two era names).

An era name was a symbol of imperial power. Declaration of another era name when one was already in use was regarded as a challenge to the current emperor. The existence of more than one era name at a time often reflected political unrest. In addition, using a particular era name was a political act implying recognition of a sovereign's right to rule, and one issue that traditional Chinese historians faced was which set of era names to use when dating a historical event. For example, when the Yongle Emperor of Ming usurped his nephew, the Jianwen Emperor's throne in 1402, he ordered all records of the four-year-reign of Jianwen Emperor to be dated as year 32 through year 35 of the Hongwu Emperor (the emperor preceding Jianwen Emperor), in order to establish himself as the legitimate successor of the Hongwu Emperor.

Era names were also employed (under different naming conventions) in other East Asian countries such as Korea, Japan and Vietnam, mostly because of China's cultural influence. They are still used in Japan. The Republic of China Era, used in China from 1912-1949, and still used in

Taiwan , marks years as Minguo (i. e. the Republic), which is usually regarded as an era name. On the mainland, era names were abolished with the adoption of the Common Era at the founding of the People's Republic in 1949.