On the self-tutorials, number 22:
audivimus cives tam fideles esse ut rem publicam conservarent: We heard that the citizens were so faithful that they saved the state.
If I'm not mistaken, 'conservarent' is reliant on 'esse' for the sequence of tenses, because it appears to me to be a part of the indirect statement. But that would mean the 'esse' is a present historical, because 'conservarent' is imperfect.
Does that mesh? Or is 'conservarent' dependent on 'audivimus', in which case I'm completely lost and would like an explanation.
Thanks!

