Hopefully Pete, or someone else, will discover what the mound was originally called but, meanwhile, the name Silbury Mound is pretty neutral and fits the bill reasonably well.
How bad's the fly-tipping? Just an idea but if the rubbish is small stuff that can be bagged and carted away in our cars maybe we could do that on the 29th after the Silbury Protest. There should be a few willing volunteers on hand and people's ideas and imput 'on site' would be interesting and valuable.
