fire emblem has a problem where it loves throwing the words "a thousand years" around without thinking of the implications
since the human mind isn't really capable of parsing timelines longer than their own potential lifespan, you hear things like "asleep for a thousand years" or "oh, rhea's been the head of the church for a thousand years" or "grima last came back a thousand years ago" and parse it initially as "a thousand years? that's basically a little longer than a hundred years"
a thousand years ago, the English language had no latinate words whatsoever. a thousand years before that, japan didn't exist. a thousand years before that, the bronze age had just collapsed.
having something be constant for a thousand years is just not something that happens in our world, so it's difficult to think of.
in terms of the real world, things a hundred years ago become semi-legendary. nobody remembers fighting in wwi, all we have are words and photographs. in an era without photography, how much would we really trust about it?
this is why people being really really weird about the 12 Crusaders in fe4 is peak fire emblem