The East half of the Roman Empire
The Byzentine Emprire lasted through what the Roman Empire fell to.
This impressive empire preserved Greek and Roman culture and connected the Silk Road to Eurpe. The Byzentine Empoire held their own against the muslims and the tough economy, the collapse of Rome made a economic depression for all of the world to occur. The Byzentine, along with a few others were able to survive. The reasons why were that theyhad an organized government, didn't get too big to manage, and minded their own business. They traded with now-a-day Russia, and hosted a Eastern Orthodox Church.