When did the Roman Empire fall (your thoughts)?

[Nathan Ross]

Then in the ensuing civil wars, when Constantine conquered all, it was a victory of Christianity over polytheism and paganism, with a new emperor and a new capitol in the East. Rome wasn't conquered by the Goths, it was conquered by Constantine and his Christians.

There was nothing un-Roman about Constantine, or his version of Christianity either! 'Paganism' by this point was veering increasingly towards a monotheistic interpretation anyway, and Constantine continued issuing Sol Invictus coins until at least 317. The 'pagan' Licinius had ordered a mass pre-battle prayer to a singular diety four years previously. Quite possibly, at the time, few people noticed the religious shift in the imperial household.

we are looking to describe a non-event. Discussions about the 'loss of centralist power in the West' or something like that would be more to the point.

Centralised power over a diverse area might be one definition of empire though... ;-)

When a new power centre arises, the empire dies - but the death can take decades.

In the modern world we're used to political changes happening very quickly and publicly - states collapse, governments fall, and new rulers stand up to give stirring speeches about the new world being born etc (Nehru's 'Freedom at Midnight' speech being the classic modern example, I suppose).

In antiquity, these sort of changes happened very gradually, and often without a lot of publicity. So, as you say, your Gallic or Spanish citizen may indeed have just assumed he was still a part of the Roman empire, until he found himself having to pay taxes to some Goth or Frankish king instead...