How long do Embassies last?

I've noticed in a few games my opposition asks to exchange embassies. Again. And I'm thinking 'Didn't we already do that?'
I know embassies are voided if you've been at war, but on these occasions there hadn't been a war - not even a denouncement!
Is there a time limit on embassies?
It's puzzling because sometimes an embassy will last the whole game (with an AI you never seem to have a problem with), yet other times I'm asked to renew an embassy exchange for reasons I can't fathom.
What factors can cause embassies to need re-establishing?

They should only be eliminated by DoW or denouncements, as far as I know.

Is it possible that earlier they gave you gold for an embassy and it wasn't an even exchange of embassies? I've done that in several games. Every so often, they give me gold again to exchange my embassy.

docbud said:

Is it possible that earlier they gave you gold for an embassy and it wasn't an even exchange of embassies? I've done that in several games. Every so often, they give me gold again to exchange my embassy.

Click to expand...

This seems like the most likely explanation to me. As Helmling said, embassies should only "disappear" after a denouncement or a DoW.

Embassies last until a denouncement or dow happens.