> Yes, they are large flat stones. I have no idea how they stay up there but
> it looks like they've been there for a long time!
Friction and compression. The stones above help hold the ones below in
place. Also, the slabs themselves often have some roughness to them
which sets up additional friction. Consider the massive weight of the
stones, it also explains why the buildings themselves are so stable.
My understanding is that for a while morter was used to bond them
together but would crack due to expansion and contraction from
temperature swings. On really steep roofs, the stones have notches and
catches and such to allow them to interlock and stay put.
--
Ken Norton
ken@xxxxxxxxxxx
http://www.zone-10.com
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