The most well-known theory tells us that Chihuahua’s were bred from an ancient breed called the Techichi, which were often used in sacrificial rituals by the Aztec People. In more recent years, after the discovery in the 1800s, the Chihuahua has been bred for almost always for companionship.
Read more
https://petfacon.com/history-of-the-chihuahua-breed/