Since six was considered a lucky number, Han Emperors Jing and Wu changed the year count of their reigns back to the beginning every six years. Since every six-year period was successively marked as "yuannian" (元年), "eryuan" (二元), "sanyuan" (三元), and so forth, this system was considered too cumbersome by the time it reached the fifth cycle "wuyuan sannian" (五元三年) in 114 BC. In that year a government official suggested that the Han court retrospectively rename every "beginning" with new characters, a reform Emperor Wu accepted in 110 BC. Since Emperor Wu had just performed the religious "feng" (封) sacrifice at Mount Taishan, he named the new era "yuanfeng" (元封). This event is regarded as the formal establishment of era names in Chinese history. Emperor Wu changed the era name once more when he established the 'Great Beginning' (太初 "Taichu") calendar in 104 BC. From this point until the end of Western Han, the court established a new era name every four years of an emperor's reign. By Eastern Han there was no set interval for establishing new era names, which were often introduced for political reasons and celebrating auspicious events.