I will discuss cosmic strings associated with axions arising from extra-dimensional gauge fields, with a focus on their impact on axion dark matter. Unlike more common 4D setups, the string cores are fundamentally singular, demanding a UV-complete description to make sense of their properties and cosmology. I will take it to be the string theory axiverse, for which one finds that the presence of cosmic strings can lead to overproduction of axion dark matter regardless of the axion mass. I will then argue that the multiple axions of the axiverse alleviate that conclusion, and that future gravitational waves observatories might probe this scenario.
