Iztlacoliuhqui, from the Codex Borbonicus. In Aztec mythology, Itztlacoliuhqui is the god of frost, cold hard things, castigation and human misery. He was previously known as Tlahuizcalpantecuhtli, who shot an arrow at the sun god, Tonatiuh. The arrow missed and the sun threw his own back at the morning star, piercing the lord of dawn. through the head. At this moment, the Lord of the Dawn is transformed into the god of stone and coldness, Itztlacoliuhqui. The Codex Borbonicus is an Aztec codex written by Aztec priests shortly before or after the Spanish conquest of Mexico. Like all pre-Columbian codices, it was originally entirely pictorial in nature, although some Spanish descriptions were later added. There is dispute as to whether the Codex Borbonicus is pre-Columbian, as the calendar pictures all contain room above them for Spanish descriptions.