Epoch is an English word that is used to describe a specific period or simply a certain era about the occurrence of events or certain places or people.
Hence, in the statement "The invention of email opened an important epoch in the history of communication."
The term which can replace epoch without changing the meaning of this sentence is ERA.
The III amendment to US Constitution places restrictions on the quartering of soldiers in private homes without the owners consent, forbidding the practice in peacetime