In Our Time turned its attention to the Sassanian Empire, a Persian empire lasting from the third to the seventh century CE. This empire was ruled by Zoroastrians, it traded with the Romans as well as the Chinese and at times defeated the Romans. Eventually it was brought down by the Muslems. It was an wonderful In Our Time again, as so often. I want to take two points that stuck with me - notnecessarily the main line of discussion.
The speakers emphasize the separation of East and West, of China and the Eurasian continent. These two power centers do not influence each other politically or militarily. What on the other hand does exist and the Western looking Sassanids take part in this actively is trade. Goods and by nature also ideas travel between the Mediterranean and China, but somehow China remains untouched by the west, even by the Sassanids, even if they traded with the Chinese themselves.
When Huns appear in history, they attack and even occupy for a moment, China first, but then, after being kicked out, they move west. The Sassanids anf the Romans face the Huns together. So far are the East and West apart that the invaders of China around 311 CE were not identified as the same as the Huns for a long time.