Simplify the following text for a Grade 6 native English-speaking person.
Original: Around AD 750 , Chang ` an was called a `` million people 's city '' in Chinese records , while modern estimates put it at around 800,000 â `` 1,000,000 within city walls .
Simplified: Around 750 A.D. Chang ` an was called a `` million people 's city '' in Chinese records , while modern estimates put it at around 800,000 â `` 1,000,000 within city walls .