What material could be used for walls on giant futuristic cities?

In the dystopic/post-apocalyptic world I'm building, civilization has been split into two different societies. One is the rich who live in very large, protected cities that have giant walls surrounding them to keep out the other society, the poor.

I haven't been able to figure out a material that would be plausible in this situation, as it would have to be strong but not top heavy and light but not fragile. Cost, time, and availability doesn't matter as it is fiction, however for the plot I am looking for a material which has a major weakness. The poor society expose said weakness in later chapters and bring the walls down in one fell swoop using something such as fire. They do not have access to extremely modern weapons or anything of the sort such as nuclear weapons.

Would it be possible, under these circumstances, to have the walls be made of an already existing material? If so, what material could be used?

posted about 7 years ago

Sydney Gish‭

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