Simplify the following text for a Grade 12 native English-speaking person.
Original: Despite a number of reforms , the Legion system survived the fall of the Western Roman Empire , and was continued in the Eastern Roman Empire until around 7th century , when reforms begun by Emperor Heraclius to counter the increasing need for soldiers around the Empire resulted in the Theme system .
Simplified: Despite a number of reforms , the legionary system survived the fall of the Western Roman Empire , and was continued in the Eastern Roman Empire until around 7th century .