The ancestors of the modern donkey are the Nubian and Somalian subspecies of African wild ass. Remains of domestic donkeys dating to the fourth millennium BC have been found in Ma'adi in Lower Egypt, and it is believed that the domestication of the donkey was accomplished long after the domestication of cattle, sheep and goats in the seventh and eighth millennia BC. Donkeys were probably first domesticated by pastoral people in Nubia, and they supplanted the ox as the chief pack animal of that culture. The domestication of donkeys served to increase the mobility of pastoral cultures, having the advantage over ruminants of not needing time to chew their cud, and were vital in the development of long-distance trade across Egypt. In the Dynasty IV era of Egypt, between 2675 and 2565 BC, wealthy members of society were known to own over 1,000 donkeys, employed in agriculture, as dairy and meat animals and as pack animals. In 2003, the tomb of either King Narmer or King Hor-Aha (two of the first Egyptian pharaohs) was excavated and the skeletons of ten donkeys were found buried in a manner usually used with high ranking humans. These burials show the importance of donkeys to the early Egyptian state and its ruler.