Ziggurats were huge pyramidal temple towers which were first built in Sumerian City-States and then developed in Babylonia and Assyrian cities as well. There are 32 ziggurats known at, or near, Mesopotamia—28 in Iraq and 4 in Iran. Notable ziggurats include the Great Ziggurat of Ur near Nasiriyah, Iraq, the Ziggurat of Aqar Quf near Baghdad, Iraq, Chogha Zanbil in Khūzestān, Iran (the most recent to be discovered), and the Sialk near Kashan, Iran. Ziggurats were built by the Sumerians, Babylonians, Elamites, and Assyrians as monuments to local religions. The earliest examples of the ziggurat were raised platforms that date from the Ubaid period during the fourth millennium BC, and the latest date from the 6th century BC. The top of the ziggurat was flat, unlike many pyramids. The step pyramid style began near the end of the Early Dynastic Period.