Once one of the major cities of the Lanna kingdom, it was originally called Wiang Hiran Nakhon Ngoen Yang and served as the capital before King Mengrai established Chiang Rai in 1262. The town was captured by the Burmese in the 16th century and sacked by King Rama I in 1803. Left a ghost town for a hundred years, it was repopulated around 1900, but still hasn't really staggered to its feet. Traces of old double city walls and many other antiquities still remain in and outside the district town.
By bus Chiang Saen is connected by bus to Chiang Rai (1.5 hrs, every 15-20 min, 37 baht). Blue songthaews also travel from Mae Sai via the Golden Triangle to Chiang Saen in about 1 hour (every 20 min or so, 60 baht).