Simplify the following text for a Grade 8 native English-speaking person.
Original: In 539 BC , the Neo-Babylonian Empire fell to Cyrus the Great , king of Persia , with an unprecedented military engagement known as the Battle of Opis .
Simplified: In 539 BC , the Neo-Babylonian Empire fell to Cyrus the Great , king of Persia , in the famous Battle of Opis .