The Silk Road officially opened some time around 200BC, when ambassadors from China turned up in Bactria and Parthia. They were looking for allies in a war, but they returned to China with tales of strange lands further to the West. Shortly after that Chinese merchant caravans started arriving in Persia, and the most fascinating trade route in history was well and truly in business.
Two things made the Silk Road possible. The first was the highway system that the Persians built. I've previously written about the King's Messengers. They could get a message from one end of the Empire to the other in an incredible three days. The main east-west arterial was called the Royal Road, but it wasn't long before it turned into the Middle East section of the Silk Road. The other building block was that the Han Dynasty took over in China. The Han assigned troops to keep the roads safe, so that traders had a chance to cross the steppes without being hit by nomad bandits.
By far the biggest trading item was the Chinese wonder-material, an astounding item called silk. Persians, Greeks, and later on, Romans, were willing to spend very large amounts of gold to get silk. (Or more accurately, the wives were willing to spend very large amounts of their husbands' money.)
My heroine Diotima acquires some silk in The Ionia Sanction, which she later uses to make a dress. I made a comment at the time that this made her the first woman in Europe to wear a silk dress. But my stories are set in the fifth century BC, and the Silk Road didn't open until the second century. Can Diotima possibly get silk 300 years before the Silk Road exists?
Yes she can. There was informal trading before the famous road opened. The reason we know this is rather interesting.
Wherever you find silk in an ancient site, you know for sure there's been contact with China, one way or another. Because China was the only source of silk.
The earliest known silk outside China occurs in the grave goods of four people in Uzbekistan (Bactria, as it was back then). The date on those graves is an incredible 1200BC. That's a minimum, they might be a few hundred years older.
Now Uzbekistan is not far from China, but it's definitely not a silk-producing region, so the silk only got there by trade. Whoever got that silk to Bactria was a serious adventurer, but it's certain someone did it. From about 500BC onwards, once the silk makes it to Bactria it can get onto the Persian road system.
The next appearance of silk comes in 1070 BC. In 1993, a team reported that they had found traces of silk in the hair of an Egyptian mummy. That's an Egyptian mummy, with silk in 1070BC!
I personally rate the abilities of ancient people highly, but even I found this hard to believe. I traced the claim. It appears in correspondence to the science journal Nature. It's correspondence, not a refereed paper, but as far as I know the claim was never refuted, but nor was the test confirmed. Nevertheless that makes the idea highly credible. That's good enough if you're a writer of historical fiction.
So it seems possible if not likely that Chinese goods were trickling into Persia and Egypt starting five hundred years before the time of Nico and Diotima.