[Ol' Dan Tucker]

But in order to increase the discomfiture of his opponent, the Goths sent an embassy into the city...

I think the correct term would be "emissary" or perhaps, "envoy?"

From the excerpt: "Vittigis, King of the Goths, hearing all this from the deserters and desiring to embroil [the Romans] with one another still more, and thinking that in this way the affairs of the Romans would be thrown into great confusion, sent to Belisarius some envoys, among whom was Albis."

[Antoninus]

I think the correct term would be "emissary" or perhaps, "envoy?"

Embassy is used here in the sense of official mission from one nation to another. I believe it may be used interchangeably with envoy in this sense.