Fantastic Crests of the Middle Ages :

The Eagle

 

In Greco-Roman mythology, the eagle was the symbol of Zeus or Jupiter, who was the king of Gods. Thus it became the emblem of the Roman emperors and their legions.  After the fall of Roman, the eagle became the symbol of the Germanic Holy Roman Empire. 

In the Old Testament the Eagle was the symbol of the all-powerful God.  In the New Testament the Eagle became the symbol of Christís triumphant Ascension into heaven. It is also associated with the Apostle and Gospel writer St. John and with contemplation and spiritual awakening.

The symbol of the eagle is commonly seen in both German and French heraldry.

Tugdual de Kermoysan was wearing for crest an eagleís head probably Gules beaked Argent (coat-of-arms : Gules, 7 scallops Argent 3.3.1.).