The Chihuahua (/tʃɪˈwɑːwə, -wɑː, -ˈwaʊ.ə/ (listen); Spanish: chihuahueño) is the smallest breed of dog, and is named after the Mexican state of Chihuahua. In a 1520 letter, Hernan Cortés wrote that the Aztecs raised and sold the little dogs as food. Colonial records refer to small, nearly hairless dogs at the beginning of the 19th century, one of which claims 16th-century Conquistadores found them plentiful in the region later known as Chihuahua. Small dogs such as Chihuahuas were also used as living heating pads during illness or injury. However, the British standard also states that a weight of 4–6 lb (1.8–2.7 kg) is preferred. A clause stating. 'if two dogs are equally good in type, the more diminutive one is preferred' was removed in 2009. A clause stating. 'if two dogs are equally good in type, the more diminutive one is preferred' was removed in 2009. Chihuahuas can be easily frightened or provoked to attack, so are generally unsuitable for homes with small children.