By the third century BCE, Chinese ironworkers were casting plough-shares in malleable cast iron, and by the Han dynasty the plough carried a curved iron mouldboard that turned and broke the soil while cutting friction. This raised yields and let one ox-team work far more land than the simple scratch-ard then used across the West. The curved iron mouldboard did not reach Europe until around the tenth century, and improved Chinese-pattern ploughs were carried to the Netherlands and England by Dutch sailors in the seventeenth century. The tool decisively lifted the agricultural surplus on which towns depended.
A more efficient plough enlarged the farm surplus that frees labour for towns, so its long diffusion westward helped raise the agrarian base beneath European as well as Chinese urban growth.