3000-1500 B.C.E.
The other day I walked into a field and noticed that it had a trenched circle in it, filled with animal bones. The next day, some men came over the hill, dragging some really big rocks. I asked them what they were making. They said, "Stonehenge." And then I realized what was going on.
I was so excited to ask them why they were making it, and the leader just grunted, "Keep track of time." Foolishly, I let them all see my watch, trying to explain that it was from the future. Before I could even get more than two words out, though, they'd snatched my watch right off my wrist and ran away.
Sorry for accidentally causing Stonehenge never to be finished...