'Great City' in the Bible

"Get up and go to Nineveh, that great city! Then cry out in protest against it, because their evil has come to my attention."

"Get up and go to Nineveh, that great city, and proclaim to it the message that I tell you."

So why shouldn't I be concerned about Nineveh, that great city, in which there are more than 120,000 human beings who do not know their right hand from their left, as well as a lot of livestock?