Where nomadic artists of the Paleolithic periods invented representation in the form of fertility figures and animal paintings, the Sumerians codified these symbols into the nature gods who served as organizing principles for their society. Predating the Egyptian pyramids, Mesopotamian temples are characterized by ziggurats (stepped platforms with sloped ramps). Many of the roots of Western civilization sprang up from the fertile river valley of the fourth millennium B.C.E. in Mesopotamia. The ancient Sumerians used the wheel and the plow, developed the earliest known script, and may well have developed the world's first formal religion; their imprint on our artistic traditions, and the imprint of the Assyrians and Persians, is no less profound. In Sumerian statuary, exaggerated eyes suggest awe of the divine, and humans are typically depicted with hands folded in prayer or holding goblets used in rituals. While the composite, rather than optical, approach continued to be the traditional mode, Babylonian artists experimented with techniques, such as foreshortening and tiered landscaping. Animals are composite as well; Lamassu, the winged human-headed bull, is one such example. In the art of the Hittites, Elamites, and Assyrians, as well as the Sumerians and Babylonians, art serves in a narrative capacity, often to catalogue in great detail the exploits of the leaders of this politically turbulent area.