How early could Chinese inventions have gotten to Europe?

Pretty self explanatory, how early could major Chinese inventions have reasonably gotten to Europe? Who would link the two civilizations?
 
Han and Rome meeting?

Actually at least governments of Rome and Han knew each others. Problem is just that trade route is long and dangerous. And Romans should go through Parthian lands.

But perhaps Marco Polo could bring some things. Or Mönke Khan's liver not fail and Batu Khan can conquer Europe and Mongols bring some Chinese inventions to Europe.
 
Maybe a few of them could have been brought over by the Nestorian monks that snuck the silk worms out of China for Emperor Justinian. The introduction of the Blast Furnace would certainly make a big difference if it was brought to Europe in the 6th century instead of the 13th. Paper making, because of it's artistic and commercial properties, might be something more likely than blast furnace designs for the monks to bring with them and would certainly add another source of revenue for the empire which would have the knock on effect of making book production easier which could certainly have some interesting consequences.
 
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