They'd probably light torches, burn people at the stake, raze crops, go on a crusade, excommunicate someone here and there until they realised they could film it all (thanks to this new TV medium) and post it on the internet (wow!) with some catchy theme music. Then they'd probably just stay in their hometowns beheading people. Of course, that was sooo 800 A.D. Some groups just have a little catching up to do.
In the rural southern part of Iraq I have seen many solitary homes and entire villages made of adobe brick by the subsistence farmers and livestock herders who built them. It looked like the set of a Jesus movie. Are thatch roofs still popular in rural Europe or Teepees in North America?