Complex sentence: In the spring of 216 BC, Hannibal took the initiative and seized the large supply depot at Cannae in the Apulian plain, placing himself between the Romans and their crucial source of supply.
Split into simpler sentences: In the spring of 216 BC, Hannibal took the initiative and seized the large supply depot at Cannae in the Apulian plain. He thus placed himself between the Romans and their crucial source of supply.