The title pairs two cities, Paris and Beirut, and the poem seems to hold them side by side in a moment of shock. We aren't told what happened, and that's part of the effect. The opening line, "the bottle of night broke," is a strange, striking image: night becomes something contained, fragile, and now spilled everywhere. It suggests a sudden rupture, as if darkness has flooded in all at once.
After that, the speaker falters. "What to do / what answer to give" reads like a mind searching for a response and finding nothing adequate. The short lines and wide gaps make the hesitation almost physical.
The last line is a question with no question mark: "is loss what the city will be for." It's bleak and unsettling, wondering whether cities exist, in the end, to be mourned. Judging by the title, the speaker may be thinking of how both places share a kind of grief. The mood is stunned, quiet, and heavy with uncertainty.