At the beginning of the Greek and Trojan war, a Trojan warrior called Cygnus, son of Poseidon, had skin charmed against the strikes of any weapon. Achilles, the fiercest Greek warrior, attempts to kill Cygnus but cannot. Realising he is unable to harm him with weapons, he brutally attacks Cygnus with armour instead, eventually virtually decapitating him with helmet straps. Taking pity on his son, Poseidon transforms Cygnus into a swan.