We are One with all there is. When the darkness of the Roman Empire grows too strong four people are brought together by those of the light to make the Empire begin to crumble and fall.

Consider the following:
I can envision an expanse of the Roman empire, but what brought these four protags together and “those of the light” is not in focus.

Check out examples in Formula (link header) to help.
When a [CHARACTER], is [confronted by a MAJOR EVENT], s/he must [do the ACTION/GOAL].
or:
A [CHARACTER], must [do the ACTION/GOAL] when [a MAJOR EVENT occurs].

Hope you find this constructive, take care.