Shennong, literally Divine Farmer, also known as the Emperor of the Five Grains (Wǔgǔ Xiāndì), is a mythical sage ruler of prehistoric China. Shennong has at times been counted amongst the Three Sovereigns (also known as "Three Emperors"), a group of mythological and sage-like emperors said to have lived some 4,500 years ago. Shennong has been thought to have taught the ancient Chinese not only their practices of agriculture, but also the use of herbal drugs. Shennong is among the group of variously named heroic persons and deities who have been traditionally given credit for various inventions: these include the hoe, plow (both leisi style and the plowshare), axe, digging wells, agricultural irrigation, preserving stored seeds by using boiled horse urine, the weekly farmers market, the Chinese calendar (especially the division into the 24 jieqi or solar terms), and to have refined the therapeutic understanding of taking pulse measurements, acupuncture, and moxibustion, and to have instituted the harvest thanksgiving ceremony (Zhaji Sacrificial Rite, later known as the Laji Rite).