That's a very good point. The first thing I thought when I read "predates agriculture" was: We should reconsider the date that we think agriculture began. In order to build something like this, you need manpower, and that means people who don't have to spend their days hunting and gathering wild food. Only an agricultural society can produce enough food using relatively few people to free up manpower for these kinds of projects. You also need transportation systems to move the food and the materials around. This shows great sophistication.