property. Shaughnessy hypothesises that this increase in the land exchanges resulted from the division of elite lineages into branches, increasing demand for land while its supply was diminishing. The 4th-century Mencius claims that the early Zhou developed the well-field system, a pattern of land occupation in which eight peasant families cultivated fields around a central plot that they farmed for a lord. Modern historians have generally doubted the existence of this idealised system, but some maintain that it may have existed informally in the early Zhou, when dependent tenants working on manorial estates paid corvée to their landlords instead of rent, as they would later. Many Chinese historians continue to describe it as historical. Handicraft industries developed during the Shang, such as textiles, bronze, and the production of weapons, were continued during the Zhou but became completely state-controlled. The Zhou government also controlled most commerce and exchange through appointing jia, officials whose title was later used to mean any merchant. Spring and Autumn period (771–475 BCE) The collapse of the Zhou initiated the Spring and Autumn period, named after Confucius' Spring and Autumn Annals. It was a time of war between states, when the earlier semi-feudal system fell into decline and trade began to flourish. Competition between states led to rapid technological advancement. Iron tools became available, producing agricultural surpluses that ended whatever had once existed of the well-field system. Towards the end of this era, the introduction of iron technology caused the complete collapse of the feudal system and ushered in a new era of development. Chinese developments in this era included the first isolation of elemental sulphur in the sixth century BCE. During the Spring and Autumn period, many cities grew in size and population. Linzi, the prosperous capital of Qi, had a population estimated at over 200,000 in 650 BCE, making it one of the largest cities in the world. Alongside other large cities, Linzi served as a centre of administration, trade, and economic activity. Most of the cities' people engaged in husbandry and were thus self-sufficient. The growth of these cities was an important development for the ancient Chinese economy. Large-scale trade began in the Spring and Autumn period as merchants transported goods between states. Large amounts of currency were issued to accommodate commerce. Although some states restricted trade, others encouraged it. Zheng in central China promised not to regulate merchants. Zheng merchants became powerful throughout