By the 6th century in the Chao Phraya River Valley, Mon peoples had coalesced to create the Dvaravati kingdoms.  In the north, Haripunjaya (Lamphun) emerged as a rival power to the Dvaravati.  By the 8th century the Mon had pushed north to create city states, in Fa Daet (modern Kalasin, northeastern Thailand), Sri Gotapura (Sikhottabong) near modern Tha Khek, Laos, Muang Sua (Luang Prabang), and Chantaburi (Vientiane).  In the 8th century CE, Sri Gotapura (Sikhottabong) was the strongest of these early city states, and controlled trade throughout the middle Mekong region. The city states were loosely bound politically, but were culturally similar and introduced Therevada Buddhism from Sri Lankan missionaries throughout the region.