With the death of Emperor Theodosius in 395 AD, the Roman Empire was split in two. Ruled by Emperor Honorius in the west and by Flavius Arcadius in the East.
This was the start of the great Byzantine Empire that would last until 1453 AD when Constantinople fell to Mohammed the Conqueror.
The Byzantine Empire has produced a style of its own in jewelry although early jewelry hardly differs from the Roman style of course.