in the Siamese language, using the Sukhothai script. The Tai Tham script was adapted to write vernacular languages not later than the 15th century CE, most probably in Chiang Mai, in the Lan Na Kingdom. The script spread from Lan Na to surrounding areas such as modern day Laos, Isan, Shan State and Sipsong Panna. Numerous local variants developed, such as the Lue variant (Sipsong Panna), the Khuen variant (Shan State) and the Tham Lao variant (Laos and Isan). The variants differ only slightly in appearance, and the system of writing has remained the same. As the name suggests, the use of the Tham (Dharma) script in Lao was restricted to religious literature, either used to transcribe Pali, or religious treatises written in Lao intended solely for the clergy. Religious instructional materials and prayer books dedicated to the laity were written in Tai Noi instead. As a result, only a few people outside the temples were literate in the script. In Isan, evidence of the script includes two stone inscriptions, such as the one housed at Wat Tham Suwannakhuha in Nong Bua Lamphu, dated to 1564, and another from Wat Mahaphon in Maha Sarakham from the same period. Most of the script is recorded on palm-leaf manuscripts, many of which were destroyed during the 'Thaification' purges of the 1930s; contemporaneously this period of Thai nationalisation also ended its use as the primary written language in Northern Thailand. Although no longer in use in Isan, the alphabet is enjoying a resurgence in Northern Thailand, and is still used as the primary written script for the Tai Lü and Tai Khün languages spoken in the 'Golden Triangle' where Thailand, Laos, Burma and southern China meet. Its use is rather limited to the long-term monks in Laos and most materials published today are in the modern Lao script. Characteristics Although both the ancient forms of the Mon and Khmer script are different, they are both abugidas that descend from the Brahmic scripts introduced via contacts with South Indian traders, soldiers, merchants and Brahmans. As a Mon-derived script, Tai Tham has many similarities with the writing systems for Burmese, Shan, Rakhine and modern Mon and rounder letter forms compared to the angled letters of Khmer. Letters can be stacked, sometimes with special subscript forms, similar to 'ຼ' which was used in Tai Noi and also in modern Lao as the subscript version of 'ຣ'