Hippos were common inhabitants of the Nile River. The animal's aggressive nature and large size worried the ancient Egyptians because they frequently went out in boats on the river. Protection against this dangerous animal was imperative, even though the hippo's habit of roaring at dawn and dusk connected the animal to the sun god. Hippo amulets appear as early as 4000 B.C. and are found through the New Kingdom. By then, the hippo had probably largely disappeared from Egypt and individual protection was less essential. Hippo amulets are made from a variety of stones, and a green stone would represent vegetation and therefore bring an association of goodness and prosperity to the wearer as well as protection.