The ancient civilizations of Mesopotamia are the source of the earliest surviving art; these civilizations were situated between the Tigris and the Euphrates Rivers. Dating back to 3500 B.C.E., Mesopotamian art was intended to serve as a way to glorify powerful rulers and their connection to divinity. Art was made from natural resources such as stone, shells, alabaster and marble, and was often created as didactic pieces. No artist signatures can be found on most of the work, because the pieces were meant to embody the subject matter, rather than the creator. Popular items that typify this time period include cylindrical seals, steles, narrative relief sculptures, and lavishly decorated tombs.