What is the origin of Southeast Asian alphabets?

The Thai alphabet may be one of the best known Southeast Asian writing systems? But where did those ornate letters come from?

Thai is one of the many Southeast Asian alphabets that originate from the ancient Brahmi script of South Asia. In spite of the difference in appearance, most of the alphabets in South and South Asia are closely related. These include Devanagari, Bangla (Bengali), Tibetan, Gurmukhi, Kannada and Telugu, Tamil, Sinhala, Malayalam, Cambodian, Burmese, Balinese, the Old Khmer alphabet and so on.

The remaining languages of Southeast Asia use writing systems derived from Arabic and Latin alphabets. Chinese characters are used by Chinese communities in Southeast Asia, and were historically used to write the Vietnamese language.