It is thought the very first wall not built around a city was erected by the Sumerian King Shulgi of Ur c. 2038. Shulgi's wall was 155 miles (250 kilometres) long and was built between the Tigris and Euphrates rivers to keep the invading Amorites out of Sumerian lands. This wall was unusual in that it did not surround a city but, rather, marked a territorial, national (rather than private) boundary and, as such, was a first of its kind. Shulgi's son, Shu-Sin, grandson, and great-grandson all tried to maintain this wall but, as it was not anchored at either end to any terminus, proved to be ineffective (one could simply march an army around either end of the wall) and finally was breached by the Elamites c. 1750 BCE resulting in the fall of Ur and the region of Sumer. Another wall of this kind, still extant, is the Great Wall of Gorgan (known as `The Red Snake' due to the red color of the bricks) in modern-day Iran. Built by the Parthian Empire (247 BCE-224 CE) it was restored and renovated by the Sasanian Persians in the 5th or 6th century CE, the wall runs 121 miles (195 Kilometres) long and included over thirty forts along its line. The wall was built as both a defensive construct and a strategic means of observing enemy deployment. It was far more effective than Shulgi's wall and it is thought that the Sasanian Persians learned the lesson of Shulgi's wall and improved upon their own. The Great Wall of Gorgon is over 1,000 years older, though far less famous, than the Great Wall of China which, though begun under the reign of Shi Huangti (ruled 221-210 BCE) was not completed in its present state until the time of the Ming Dynasty (1368-1644 CE). Like the Great Wall of Gorgon, the Great Wall of China was built as a free-standing structure for defense of a region as was the Anastasian Wall (also known as The Long Walls of Thrace) of the Byzantine Empire (begun c. 469 CE) located in modern Turkey.