[SunkenCiv]

http://www.freerepublic.com/tag/charlemagneevent/index

http://www.freerepublic.com/tag/fusamiyake/index

http://www.freerepublic.com/tag/iron60/index

[Bob Ireland]

***the likely source of the medieval cosmic ray bombardment—a coronal mass ejection from the Sun***

And others say the super nova; I tend towards the larger cosmic event - but what do I know? Let the Transformers work it all out.