[blam]

"You seem to place some mythic significance upon 540AD. "

Nothing mythic, hard data. The trees worldwide recorded something catastrophic at that time +- 4.0 years. I submit that the Dark Ages were so named because it was dark. A dust veil around the entire earth.

[Burkeman1]

The "dark ages" were not called that until modern times. People in 550AD didn't walk around and say- gee it looks dark. Modern scholars applied that term to describe the loss of learning and knowledge from most of Western and Northern Europe when the Romans began to pull back. For example- English historians pinpoint the start of the "dark ages" in Britian at 411AD- when the Romans left. And even though most historians would argue the dark ages ended around 1000AD (this is an argument) and the Medevil period began- Britian did not attain the same level of technology, adminstration, and economy it had enjoyed under Rome until the late 16th century.