Question

The ostrogoths' kingdom was separated from central europe by the -select- , while the anglo-saxons' kingdom was separated from the rest of europe by the -select-

Answer 1

The Ostrogoths' kingdom was separated from central europe by the ALPS, while the Anglo-Saxons' kingdom was separated from the rest of Europe by the -ENGLISH CHANNEL -- as we would call it today.  Then they might have called it by the ancient name (from Ptoltemy) - "Oceanus Brittanicus" or the Anglo-Saxons would have called it the "South Sea."