In addition to the emperor and the empress, the Aztecs had a complex social hierarchy that included nobles, priests, warriors, merchants, and commoners. The nobles were the highest-ranking members of society and were often related to the tlatoani. The priests were responsible for religious ceremonies and were considered to be intermediaries between the gods and the people. The warriors were a professional military force that was responsible for defending the empire. The merchants were an important part of the economy and were responsible for trade and commerce. The commoners were the lowest-ranking members of society and were often engaged in agriculture or other forms of manual labor.