This massive stupa, rising more than 120m, is one of the tallest Buddhist monuments in the world. Its name in Sanskrit roughly translates to 'first monument', an indication of its ancient status among Thailand's religious structures. Exploring the site is a pleasant and calming experience; you can easily spend a couple of hours within the complex admiring the massive dome, visiting smaller shrines and watching devotees immersed in rituals and worship. The stupa is just south of the railway station.
The original structure was erected in the early 6th century by the Theravada Buddhists of Dvaravati. But, in the early 11th century the Khmer king, Suriyavarman I of Angkor, conquered the city and built a Brahman prang (Hindu/Khmer-style stupa) over the sanctuary. The Burmese of Bagan, under King Anawrahta, sacked the city in 1057 and the prang lay in ruins until Rama IV (King Mongkut) had it restored in 1860.
On the eastern side of the monument, in the bòht (ordination hall), is a Dvaravati-style Buddha seated in a European pose similar to the one in Wat Phra Meru in Ayuthaya. It may, in fact, have come from there.
Also of interest are the many examples of Chinese sculpture carved from a greenish stone that came to Thailand as ballast in the bottom of 19th-century Chinese junks. Opposite the bòht is a museum, with some interesting Dvaravati sculpture and lots of old junk. Within the chedi complex is Lablae Cave, an artificial tunnel containing the shrine of several Buddha figures.
The wát surrounding the stupa enjoys the kingdom's highest temple rank, Rachavoramahavihan; it's one of only six temples so honoured in Thailand. King Rama VI's ashes are interred in the base of the Sukhothai-era Phra Ruang Rochanarit, a large standing Buddha image in the wát's northern wí·hăhn (sanctuary).