Building a monument out of your local rock doesn't seem like a coincidence at all to me.
As I understand it, Silbury is built on a spur of chalk sticking out in the fertile flood plain so doesn't represent an intention to sacrifice good land, quite the reverse.
The connection between c*nt and fertile place..... now THAT seems like mere coincidence, stretched beyond reason, one being biology and one being geography.
The only matter yet to be resolved as being a coincidence or otherwise is why aggressive or trolly postings always get posted between 10.00 and 11.00pm at night. I wish they weren't.