Each era name has a literary meaning. For instance, the first era name of Emperor Wu was Jianyuan, literally meaning “establishing the Origin”. Era names also reflected characteristics of political and other landscapes at the time. , the first era name of Emperor Huizong of Song China, means “establishing middle, peaceful 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”. Popular phrases might be repeated, as with the numerous Taiping eras (lit. “Era of Great Peace”).
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, literally meaning “change the Origin”.
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, 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 Emperor Wu and Jin Kangdi picked Jianyuan as their motto. Thus AD 344 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 Emperor Wu). In traditional literature, one can therefore find references like “the first month of the thirteenth year of Jianyuan”.