Thailand's oldest kingdom was built around the city of Sukhothai, Sukhothai. Sukhothai was the capital of Siam and north of northern Thailand. It was the earliest kingdom, and it reached between the 13th and 14th centuries.
In the 13th century, Sukhothai was part of the Khmer Empire. Thai Rulehood became known when two Thai chieftans Pho Khun Pha Muang and Pho Khun Bang Klang Hao declared their independent independent kingdom in Thailand. Sukhothai's first king was Pho Khun Bang Klang Hao, who also called Pho Khun Si Indrathit or Intradit.
Sukhothai's kingdom expanded and allied with other Thai kingdoms. The Theravada Buddhism they adopt is their state religion. Pho Khun Bang Klang Hao's son succeeded after the throne. Later his brother, Pho Khun Ramkhamhaeng, took over the throne. During his reign, Sukhothai lived gold and flourished.
Ramkhamhaeng introduced the first Thai letters. During his time the kingdom extended and spread over a large area of Marta (today Myanmar) to Luang Prabang (today Laos) and down to the Malay Peninsula. The kingdom was bigger than modern Thailand.