Gavmishan Bridge  Gavmishan Bridge is a historical bridge in Darreh Shahr County, Ilam Province, Iran. The bridge was built in late Sasanian era on Karkheh River, parts of which constitutes the modern-day border of Ilam and Lorestan provinces. It is in length and about in width. It has the longest arch span among the ancient bridges in Iran. It is known by many experts as an engineering feat considering the time it was built, the material used and the floods it has withstood during its age of 1400 years. It is believed that the bridge was intentionally destructed by the Persian Army to stop or slow down the invasion of Arabs during the Muslim Conquest of Persia in the 7th century. The bridge passes Karkheh river, which is the confluence of Seymareh and Kashkan rivers. Nowadays, Seymareh and Karkheh indicate the eastern border of Ilam Province. It is 20 km east of Darreh Shahr, and 30 km from Pol-e Dokhtar, near the modern bridge. According to texts, the bridge was once restored by Vaali of Posht-Kooh about 200 years ago. Being on the border of Ilam and Lorestan provinces has resulted in many disputes regarding ownership of the bridge. Nevertheless, the latest restoration took place between 2005 and 2008 by funding from the Ilam province.