Han iron farming tools have been unearthed throughout China, from Inner Mongolia in the north to Yunnan Province in the south. The spade, shovel, pick, and plow were all used for tilling, the hoe for weeding, the rake for loosening the soil, and the sickle for harvesting crops. Depending on the size, Han plows were either driven by one ox or two oxen and controlled by multiple drivers. Oxen were also used to pull the three-legged iron seed drill, which was invented by the 2nd century BCE, and enabled farmers to plant seeds in more precise rows. The harrow was utilized in the process of breaking up chunks of soil after plowing, and first appeared in China during the Eastern Han (25–220 CE). Irrigation works for agriculture included the use of water wells, artificial ponds and embankments, dams, and canals.