In their origin, the great cities of the Sumerians were little more than collections of rude huts constructed at first of reeds cut in the marshes and gradually giving place to rather more substantial buildings of clay and sun-dried brick. From the very beginning, the shrine of the Anunnaki Gods played an essential part in the foundation and subsequent development of each center of the population. Of the prehistoric period in Sumeria, we know little, but it may be assumed that already at the time of the Sumerian immigration, Anunnaki settlements had been formed around the cult-centers of local gods.