The eagle is used in heraldry as a charge, as a supporter, and as a crest. Heraldic eagles can be found throughout world history like in the Achaemenid Empire or in the present Republic of Indonesia. The European post-classical symbolism of the heraldic eagle is connected with the Roman Empire on one hand (especially in the case of the double-headed eagle), and with Saint John the Evangelist on the other.
A golden eagle was often used on the banner of the Achaemenid Empire of Persia. Eagle (or the related royal bird vareghna) symbolized khvarenah (the God-given glory), and the Achaemenid family was associated with eagle (according to legend, Achaemenes was raised by an eagle). The local rulers of Persis in the Seleucid and Parthian eras (3rd-2nd centuries BC) sometimes used an eagle as the finial of their banner. Parthians and Armenians used eagle banners, too.
In Europe the iconography of the heraldic eagle, as with other heraldic beasts, is inherited from early medieval tradition. It rests on a dual symbolism: On one hand it was seen as a symbol of the Roman Empire (the Roman Eagle had been introduced as the standardised emblem of the Roman legions under consul Gaius Marius in 102 BC); on the other hand, the eagle in early medieval iconography represented Saint John the Evangelist, ultimately based on the tradition of the four living creatures in Ezekiel.
In early heraldry or proto-heraldry of the 12th century, however, the eagle as a heraldic charge was not necessarily tied to either imperial or biblical symbolism. The Anglo-Norman L'Aigle family, who held Pevensey castle and the Borough of Pevensey used the eagle as an emblem in an instance of canting arms. The earliest known use of the eagle as a heraldic charge is found in the Great Seal of Leopold IV of Austria, dated 1136. Adalbert I, Duke of Teck used an eagle in in 1190.
By the late medieval period, in German heraldry the eagle developed into a symbol of the Holy Roman Empire, and thus became comparatively rare outside of coats of arms derived from the Imperial Eagle.