Anthropologists refer to those with formal, inherited positions of community leadership as chiefs. Over time, a chief can expand their dominion to incorporate several towns and villages into a small chiefdom. Chiefs may form political alliances with other regional chiefs in large pyramidal systems consisting of various levels of village chiefs and regional chiefs, with one very powerful chief at the top. When a chiefdom expands to encompass multiple ethnic groups in a regional empire, the leader is referred to as a king. Chiefdoms are a very common form of political organization, found in historical and contemporary societies all over the world. Archaeologists and cultural anthropologists have discovered chiefdoms in Africa, Oceania, the Middle East, Europe, East and Southeast Asia, and North, Central, and South America. While there is considerable diversity in the way these various systems of chieftaincy operate, anthropologists have identified a set of elements common to many of them. The fusing of multiple forms of power is the defining feature of chiefdoms, common to all of them. Economic, political, religious, and military power are all concentrated in the position of the chief. In Mesopotamia, the cities of Sumer were initially ruled by religious priests who represented local gods and oversaw work on common lands. Over time, priests began to share their power with secular governors who maintained law and order, managed the economy, and led military campaigns. Eventually, religious and civil power became fused in the office of the lugal. As lugals solidified their power, they began passing down their office to their sons, establishing dynasties. Central to the power of a chief is control over economic resources such as land, agricultural surplus, and trade. Chiefs often hold land in public trust, determining who may farm where and also allocating farmland to newcomers. They have their own farming plots, commanding regular public labor to work on them. Farmers are obliged to channel a portion of their surplus to the chief, who holds it in storage facilities for public feasts or distribution to those in need. Chiefs regulate local trade and negotiate regional trade networks to benefit their own communities. They control the production and distribution of certain prestige goods, such as royal textiles and ornaments made of jade, gold, copper, or shell.