original: during its heyday , chang ' an was one of the largest and most populous cities in the world .
simplifications: during its prime time , chang 'an was one of the largest and most crowded cities in the world . during its heyday , chang ' an was one of the largest and most populous cities in the world . ghang ' sn was on of the largest most popluated cities in its heyday . during its heyday , chang 'an was one of the largest and most populous cities in the world . during its peak , chang 'an was one of the largest and most crowded cities in the world . during its heyday , chang ' an was one of the largest and most populous cities in the world . during its heyday , chang 'an was one of the largest and most populous cities in the world . chang 'an was one of the largest and most populated cities in the world .