What did the Romans do to help protect most cities from attack?
They built them on hills.
They surrounded them with canals.
They bordered them with farmland.
They constructed walls around them.

They built them on hills.

Explanation:

Of course, they did this to create a natural defense from the attack of foreign invaders. For example, the city of Rome itself was built on seven famous hills. Of course, through time they tried to fortify them as much as possible, but the main defense laid on the physical location of those cities.