BBC News - Roman rise and fall 'recorded in trees'

via bbc.co.uk

Similarly, there was a great program, perhaps on the History channel a few years back about Pompeii, a German I think, archeologist found in excavating, that it was actually a dust cloud of Volcanic ash that killed the people in the city, not the lava as generally believed. He found that there was a thin layer of sediment in the ground at the time the eruption occured, and theorized that the city was eveloped in dust, and people were unable to breathe and died.