Partly because my Vogue Knitting holiday issue seems to have disappeared (it may be time to clean the house), and partly because HistoricStitcher left me a comment about it (you can read it, here.)
In a nutshell, she makes a case for knitting being brought to Europe during the Crusades, by returning camp followers and the like, who'd gone to the Middle East.
I do think that the Crusades did trigger the movement of knitting, along both trade routes we've discussed before; across N Africa into Spain, and up through the Black Sea into Eastern Europe. There were probably a lot of refugees from the fighting, and they'd have moved along those trade routes to get away from it. Stands to reason.
It's likely there were also all kinds of single bits of knitting brought back by the Crusaders, shirts and socks and gloves and all, and spread out all over Europe. Archeology just hasn't found them. Most were probably worn to rags, and the rest lost in the coming thousand years.
But the thing is, knitting isn't just a trade good, it's a SKILL, something that has to be taught, and learned, to be truly passed along. And it's more the skill of knitting and it's movement, than plain old knitted socks, that I'm talking about. There were other things that the Crusaders brought back to Europe, that are well-documented - spices and citrus fruit leap to my mind, thanks to the food research I do - and both of those goods exploded onto the scene, historically speaking. Looking back, it's like one minute, no one in Europe had heard of them, and the next, every rich person from Ireland to Moscow was eating cinnamon-orange pudding. Blam. Sudden influx.
Knitting's movements weren't like that. There's no sudden appearance. It can be tracked across Europe (at least Western Europe) pretty easily, looking at paintings and fragments and linguistics. It took hundreds of years to spread all the way to Scandinavia, from Spain, which is kind of what you'd expect of a skill that has to be learned. (Iron working, which was only invented once, in China, and then spread west to India, the Middle East, and Europe, can be tracked much the same way, though it took longer to move, because it traveled further.)
So... Crusades and knitting. Yeah, I bet the Crusades did have an effect on knitting's movement. But I still don't think the skill was brought back by returning crusaders, at least not in numbers large enough to matter. Certainly it's possible, even probable, that single people returned with the knowledge, and may explain odd bits and pieces that have been found. But knitting as a trade? That took some time.