Question

How did the boundaries of the Byzantine Empire change

Answer 1

Over its history, they expanded and shrank with conquests and defeats like any empire back then. At the end, the Byzantine empire had shrunk down to a small area around its capital, Constantinople, a few islands, the Peloponnese peninsula. Compared to what it had a few centuries earlier under Justinian in the 6th century (it nearly surrounded the Mediterranean), this was a tiny fraction of what it used to be.