The population of the Roman Empire at its peak in 117 AD was between 59 to 76 million
at that same time, Han China (which had a census in 156 AD) was about 51 million people
Estimates are that Caesar’s conquest of Gaul involved killing about 1 million Gauls.
The Romans just slaughtered anybody that opposed them.
Jack the Ripper wouldn’t recognize the people living in Whitechapel these days.