How did ideas and inventions travel along the Silk Road?

Picture a road so long it isn't really one road at all. It's a web of dusty paths stitching China to the Mediterranean, threading over mountains and across deserts. We call it the Silk Road, and yes, silk traveled on it. But silk was the boring part. The truly exciting cargo was invisible: ideas.
Here's the first thing to understand: almost nobody walked the whole road. A trader from China might carry his goods a few hundred miles, sell them at a market town, and turn around for home. Someone else picked them up and carried them a little farther. The road worked like a bucket brigade — passing things hand to hand, town to town, until they ended up oceans away from where they started.
