Answer:
Relied on enslaved labor in cities is the correct answer.
Explanation:
~<span>Most </span>slaves<span> during the </span>Roman<span> Empire were foreigners and, unlike in modern times, </span>Roman slavery<span> was not based on race. </span>Slaves<span> in </span>Rome<span> might include. Another </span>difference between Roman slavery<span> and its more modern variety was manumission;the ability of </span>slaves<span> to be freed.
Hope this helps.</span>
Your answer would be population density.
The word "unique" means something that is unlike anything else. In urban areas, it's mostly heavily populated due to the amount of residential, business, and suburban areas. Urban areas are packed with houses, apartments, businesses, and etc. When you go into the country side of town, they're not heavily populated due to it being mostly land and not residential places.
