One of the most brutal tactics of ancient warfare was the concept of the siege.
Instead of breaking down the gates, firing burning arrows, or releasing a large mythical beast into the city, there were times when an enemy army would set up a siege against their helpless adversaries. A siege is a waiting game that requires blocking all the entrances and exits in a city and making sure nothing gets in or out. This is would be like an ancient version of being sent to your room except a good siege always made sure that access to water and food was also completely shut off. So in a siege all an enemy army had to do was set up camp nearby, place a few guards to watch for escapees, and wait for the city they were trying to conquer to starve to death.
Given that you can technically go 30 days without food and the fact that the city would have had some food in reserve within its gates you can imagine that this would take awhile.
The people of Samaria in 2 Kings chapter 6 and 7 found themselves in such a situation.