What was the worlds population in the first century?

Answer 1

Let's make a beginning. The population of Rome was 500,000. The population of Gaul or Britain was a very few million. The number of Romans who went to Gaul or Britain just after Julius Caesar was a few thousand. The Romans were much diluted by the Celts, although they ruled over them. So the world's population was "several," although they were ruled over by a few.

Answer 2

1 AD 300 000