Herodotus reliabily is a big debate in itslef.

In the Bible, in Jonas' Book, it is said that the city's population is over 120 000 and that 3 days of walk are needed to cross the city.

Is it a confirmation? In itself, no. But according to A. Tenu (CNRS), the city surface is estimated at 8 square-km, only Babylon was bigger is the area with 10 square-km.

Of course, with a l high density, it possible to reach 100 000 people. Paris would be roughly 400 000 in 1630 after recovering from the plague while being slightly larger than 8 square-km. But thats another place in another time.

Rome would have a far greater population 700 years later (1 million?) but if we try to imagine Niniveh after 706 BC, when the city was chosen as the new capital, it is plausible for the city to sustain a huge population as new aqueducs were built and fields were extended.

After all, it seems that the city had enough water to make the hanging garden possible. According to S. Dalley in The Mystery of the Hanging Garden of Babylon, Nabuchodonosorus II would had built it there and not in Babylon, where no record if it have been found.

Are we sure of the population size in the 8th or 7th century BC? No.

Does the surface make it possible? Yes.

Does the city had enough ressources to feed a large population? The archeological traces seem to say so.

Does the city had such a density to reach a 100 000+ population. Currently we are less sure.

Could the city have reach a 100 000 population? My cat know as much as me I think.