Maybe it is me, who misunderstood something, but in the description section, the second part of the sentence suggests that the "ancient power" is actually gone, but the first part is in present perfect which suggest is it still there. I'm not a native English so maybe I'm wrong, but it does not make sense for me. For me, it would be more logical as "Even though the ancient power used to inhabited this place is long gone, its presence still echoes in the halls of the city."