Complex sentence: A Migration period sword was a type of sword popular during the migration period (4th to 7th centuries AD) show a transition from the Roman era Spatha to the Viking sword-type of the Early Middle Ages, which eventually gave rise to the arming sword.
Split into simpler sentences: A Migration period sword was a type of sword popular during the migration period (4th to 7th centuries AD). This sword type shows a transition from the Roman era Spatha to the Viking sword-type of the Early Middle Ages, which eventually gave rise to the arming sword.