Even in its beginnings, ancient Rome was never that _________; a constant influx of settlers, immigrants, tradesman, and slaves ensured a _________ of people.
In this questions, shouldn’t be even in be a contrast word for second blank?
Hey there, I think you are on the right track in trying to identify the “support/contrast” keywords. However, you should not be locked into thinking of it in a binary way. Contrast can refer to extreme things such “even in”… Hope that helps you to re-attempt the question with fresh eyes 
Another way to think about this question: does the phrase “Even in its beginnings” contribute to the core meaning of the sentence or could it be dropped entirely with no significant change in meaning? You can simply ignore this phrase, so it doesn’t serve as a meaningful contrast in this particular sentence.