Simplify the following text for a Grade 12 native English-speaking person.
Original: The Byzantines , however , managed to stop Islamic invader from moving further into their lands during the 8th century and , beginning in the 9th century , took parts of the conquered lands back over .
Simplified: The Byzantines , however , managed to stop further Islamic expansion into their lands during the 8th century and , beginning in the 9th century , reclaimed parts of the conquered lands .