It initially appears as a ruined building and it can be repaired starting in the Medieval Age in order to unlock its functionality.
Upgrading it can increase the capacity of Coalitions.
Unlike the standard buildings, you cannot move it.
The Embassy cannot be destroyed in battles.
Coalitions can be formed while the Embassy is being upgraded; but they must be formed via the war screen instead of from the Embassy itself.
Offensive coalitions can be formed after the war's attack stage begins, and also used between attacks.
A foreign Embassy is the official office of one country in the capital of another country. It is where the ambassador(representative) of the home country works and it is where most of the communication(talk) between the two governments happen.