Where did they come from?
Many people left Georgia and Armenia about that time and moved to Iran and northern India. So the Sogdians were Indo-Europeans, like their Persian and Indian neighbors. Their language was closely related to Persian. Like other Indo-Europeans, they brought their horses and chariots with them. Their main city was Marakanda (now Samarkand).
The Sogdians and the Persian Empire
Cyrus the Great conquered the lands around Persia to form the Persian Empire in 526 BC. One of the kingdoms he conquered was Sogdiana. After that, the Sogdians were part of the Persian Empire until 325 BC. They had a big fort called the Sogdian Rock or the Rock of Arimazes. Near this fort, at Takhti Sangin, there was a magnificent collection of gold and silver. We call it the Oxus Treasure.
Why were the Sogdians rich?
Probably the reason they had so much gold and silver was that they were traders. They sold their horses and cattle to China and Persia. And they also sold Chinese silk to Persia. They sold Persian silver and glass beads to China.