Simplify the following text for a Grade 9 native English-speaking person.
Original: The size of a typical legion varied throughout the history of ancient Rome , with complements of 4,200 legionaries and 300 equites ( drawn from the wealthier classes - in early Rome all troops provided their own equipment ) in the republican period of Rome , ( the infantry were split into 30 maniples of 120 legionaries each ) , to 5,200 men plus auxiliaries in the imperial period ( split into 10 cohorts , 9 of 480 men each , plus the first cohort holding 800 men ) .
Simplified: It had a complement of 4,200 legionaries in the republican period of Rome . In the imperial period , the full complement was 5,500 men split into 10 cohorts of 480 men each .