I found this example sentence in the Internet.
I have learned to do as the Romans when in Rome.
What I don't understand is, why use 従え? Shouldn't it be 従い?
Is there any difference in meaning between the two?
従え is an imperative form of 従う. Cf. https://en.wikipedia.org/wiki/Japanese_verb_conjugation#Imperative
従え = "(please) do follow the rules of this place (郷)."
I guess it is similar to 従いなさい, though I've never read it in this form.