Though not as well known as the Great Wall of China, Sassanian Iran (in the centuries before the coming of Islam) was once protected by the Great Wall of Gorgan, protecting northeastern Iran from steppe peoples of Central Asia. With other fortifications to the west of the Caspian, Iran was protected by a network of defensive walls rivaled in length only by their more famous Chinese counterpart. The eastern and western walls protecting the "Caspian gates" came to be associated with the mythological tales surrounding Alexander the Great and the so-called Wall of Gog and Magog.
Iran is now talking about erecting a wall of another sort, a firewall against the world, apparently as part of its declared intention of creating a national Intranet independent of the global Internet. It's latest step:
Iran has cut off access to Google and Gmail, Officially, the moves against Google were in retaliation for YouTube's not taking down the controversial film attacking the Prophet. YouTube is owned by Google.
Most access to Facebook, Twitter and other social media has been blocked for some time.
Iran claims its attempt to create a self-contained national Intranet is not primarily aimed at isolating its people from information, but at blocking the sort of cyber-attacks on its computer and scientific infrastructure, including its nuclear program, that it has experienced in recent years.