The term "great power" has only been used in historiography and political science since the Congress of Vienna in 1815.[1] Lord Castlereagh, the British Foreign Secretary, first used the term in its diplomatic context in 1814. Use of the term in medieval historiography is therefore idiosyncratic to each author. In historiography of the pre-modern period, it is more typical to talk of empires (itself a poorly-defined term, see list of empires).