One of the holiest buddhist monuments in Thailand, Wat Phra Pathom may house the oldest Buddhist structure in Thailand. According to the legend a chedi was erected during the period of a Mon-kingdom in the 2nd century. Although the structure has a similar style to the Sanchi Chedi in India which was built in the reign of King Asoka. This would date the place back to the year 539 AD. You cannot see the original chedi because it has been encased by the new chedi and nobody is allowed inside. However, some ornaments, statues and other objects from different periods are on display along the outside of the chedi.
The present Phra Pathom Chedi was built during the reign of King Rama IV in 1853, under his royal command, the new Chedi was constructed to cover the former Chedi of which the shape was of an upside down bell shape with a Prang top. The construction of the new huge Chedi was completed in the reign of King Rama V in 1870 AD. Today this is the largest chedi in Thailand and one of the largest in the world. In all, it took 17 years to build.