Which essential urban need was met by structure made possible by roman engineering

I believe the answer is: the arc building was for clean water

Through this building, people in roman empire able to obtain water from the resources that located outside of their empire and provide necessary nutrients for their crop to grow. The clean water was also used to support various other Roman economic sector, such as gardens, mining, blacksmith, animal husbandry, etc.

lincoln declared that slavery should not be allowed to spread into the new states, and of course this angered the south at the time.

arresting and exicuting citizens