In the July, August/08 issue of Archeology is an article titled, "The Shah's Great Wall", by Eric A. Powell. It refers to a wall which extends 30 miles, from the foothills of the Caucasus Mtns., to the Caspian Sea, and has 60 fortresses built into it, as well as a few towns. The Scythians invaded the Near East through this pass, and realizing its importance, the Sasanians built this wall onto the fortress at Derbent, where the plains narrow down to their skinniest location. This construction started in 570 AD. The hill around the city has been settled since the Bronze Age, and it was a fortified city in the 8'th century BC, but if they wanted to stop the invasions, a wall was probably required. You know the old saying, "fences make great neighbors". This one is about 20 feet tall. When the Byzantines backed the Khazars against against the Sasanians, they were able to seize Derbent, and just a few years later, the Sasanian Empire disappeared. Three other walls, but made of mud bricks, were built about 50 years earlier, also as defenses against nomadic tribes of the north. One of these started at the east coast of the Caspian and went about 120 miles east. This one was known as the "Wall of Gorgon", and seems to be the wall reported on in the previous post. Interested readers should check that link as well. Another was the "Great Wall of the Caucasus", known locally as Dag Bahri, or "Mountain Wall". Another was built in Azerbaijan, called Ghilghilchay or "Wall of Clay". It was 60 miles long. Oddly, the "Great Wall of China" is thought to have been built to defend China against the Huns, while centuries later these other walls were built to defend the Sasanians against several nomadic tribes including the Hepthalites, otherwise known as the White Huns. The "Great Wall", the stone one was still in use in the 19'th century.