The Greco-Bactria
While everyone talks about the life and adventures of Alexander the Great, no one really talks about the men who followed him into battle, post-conquest. After Alexander died unexpectedly, his generals fought over his conquered lands and divided it up amongst themselves. The most well-known Empire that came out of that was the Seleucid Empire, but no one really talks about the splinter state of Greco-Bactria (near modern-day Afghanistan).
This Empire became so powerful by the Third Century BC, that it declared independence from the Seleucid Empire and became known as the land of a thousand cities. They were at the centre of a fusion of Persian, Indian, Scythian and Greek cultures. It was considered a virtual paradise until it came under attack a century later, and the people were forced to scatter.
Ruins of the capital city Alexandria on the Oxus (now known as Ai Khanoum), were still evident up until 1978 when the Soviet-Afghan War destroyed the site.