During this period, the Aryans were a tribal people primarily engaged in farming and herding. Merchant and artisan classes had begun to appear, although large cities had not yet developed. Labor was becoming more specialized. Society was divided into four classes, called varõa (colors). At the top were two classes: the priestly class (bràhmarna),composed of those who sacrificed to the gods, and the ruling caste (ksatriya),composed of rulers and warriors. Below them was the vaisya class, composed of farmers, herders, merchants, and artisans. The duty of the slave class (sådra) was to serve the other three classes. Eventually the system became more specialized and produced the many divisions that make up the caste system today. A member of one class was usually not allowed to marry or even eat with someone from another class.