The two sentences below are examples of metaphors:
The border is a moat but without a castle on either side.
The border is a locked door that has been promoted.
Explanation:
The metaphor is a figure of speech that seeks to establish a comparison between two elements, subjectively, that is, this comparison is not made explicitly, but relates a common characteristic between the two elements.
In the case of the phrases presented above, we can see that the poet used the metaphor to compare borders with an unowned owner and an open door. He did this to reinforce the idea that borders are not designed to separate and limit us, but rather to unite us and make us a global, unified people.
