At Left: Tap O’Noth, Inverurie Scotland. - Right: Arbory Hill, South Lanarkshire Scotland.
At To'N it looks as if a giant concrete mixer poured a batch of semi molten rocky material onto the bare hilltop, before some super sized device imprinted the viscous matter to make the flat inner area..
It seems that whatever caused the imprint at lower right on the 2006 NASA's Mars Reconnaissance Orbiter image above, would be about the only thing up to the task, while the amount of semi molten material required to construct the triple battlements on the Arbory Hill monument, continues to boggle the mind.
There are over one thousand similar hillforts scattered about in England and Scotland, a similar fort with seemingly vitrified walls appears in the NASA Mars Rover Image of Mount Sharp above, all of which supports the contention the vitrified hillforts on both planets were built by space travellers.