In the Han Buddhist temples, usually the images of eighteen Arahats can be seen. Who are they？In fact, there should be sixteen arahats, or sixteen āyamas (Arahat is transliterated into Chinese as Aluohan, or simply Luohan0. According to the Buddhist canons, under the Buddha’s instructions, sixteen of his disciples would not enter into Nibbāna. In Nandimittāvadāna written by Āyasma Nandimitra of Siharatta (now Sri Lanka) In The 2nd century AD, The names of the sixteen arahats and localities of their residences were recorded. After the book was translated into Chinese by Dhammācāriya Xuan Zang, the sixteen arahats were held in universal esteem by the Chinese Buddhists. By the time of the Five Dynasties, with the growing popularity of paintings and sculptures, representation of sixteen arahats was gradually superseded by representations of eighteen arahats. Presumably the painters intended to add Nandimitra and Xuan Zang, the writer and the translator of Nandimittāvadāna into the list. However, when later generations put the names of Arahats on the paintings, Nandimitra was mistakenly listed as the seventeenth resident Luohan, and the name of the first Arahat was repeated as the eighteenth. Though this mistake was already found out in the Song Dynasty, the formulation of the Eighteen Luohans became wide spread in China, probably because of the many inscriptions and paintings made by famous calligraphers and painters as well as men of letters such as Guan Xiu, Su Dongpo, and Zhao Songxue. (From  Essentials of Buddhism）