Now, archeologists think they have found it. Was it moved to some other religious site by cultists? Did a UFO come back to claim it?
No, it appears somebody a few centuries ago just dragged it away because they were short of rocks for their construction project. The altar has apparently been found, in two pieces, as part of a small bridge a few miles down the road.
What were they thinking?
Well, nobody really knows. There's not exactly a shortage of rocks in England.
For some reason, the English seem to just enjoy building mundane shit out of important historical artifacts, like they did with Hadrian's Wall. That's a 2,000 year-old wall across Northern England originally built by the Romans, the bricks of which now can now be seen in nearby houses and churches.
But some old brick wall is one thing; Stonehenge has stood unmolested for nearly 5000 years, and even in the 1600s people knew how important it was. It takes a lot of English balls to steal a huge rock from a mystical ancient site just because you can't be assed to cut a couple more stones for your little bridge.
"Ah, just grab one from over there."