What happened to the Bronze Age people do not know. Thais probably came not to the area that today is Thailand until the 1000's. In the late 1200s founded the kingdom of Lanna ("the land of million rice fields"), in what is now Thailand's northern part. Chiang Rai was first elected to the capital, but when King Mengrai saw five white mice, two white sambarhjortar and two white deer along the banks of the Ping River, he took it as an omen and moved his capital to Chiang Mai. Mengrai reigned successfully into its 80th year, when he was killed by lightning.
Ang Thais ay marahil hindi naparito sa lugar na ngayon ay Taylandiya hanggang sa 1000 ni. Sa huli 1200s itinatag ang kaharian ng Lanna ("sa lupain ng milyong palayan"), sa ano ngayon ay hilagang bahagi ng Taylandiya. Chiang Rai ay unang inihalal sa kabisera, ngunit kapag nakita Hari Mengrai limang puting Mice, dalawang puting sambarhjortar at dalawang puting usa kasama ang mga bangko ng River Ping, kinuha niya ito bilang isang tanda at inilipat ang kanyang kabisera sa Chiang Mai. Matagumpay na naghari Mengrai sa 80 taon nito, kapag siya ay namatay sa pamamagitan ng kidlat.