The Ziggurat - The temples of Mesopotamia were called ziggurats, a type of stepped pyramid with terraces. The terraces were accessed by ramps leading up to the upper levels. Unlike the Egyptian pyramids which were made of granite, ziggurats were constructed of baked mud-bricks. It's hard to say when they first began to be built.  Many Biblical scholars believe the "Tower of Babel" was a ziggurat, indicating that they may predate history.  The oldest surviving of these temples dates from the late 3rd millennium BC, though they are probably centuries older than that.