Sukhothai, First Capital of the Kingdom of Siam
Sukhothai was the first capital of the Kingdom of Siam. Active in the 13th and 15th centuries. It was a powerful capital and the artistic style of its Buddhas and architecture are known as Sukhothai style today. It is a UNESCO World Heritage site.
Ayutthaya, Second Capital of the Kingdom of Siam
The Historic City of Ayutthaya was the second capital of the Kingdom of Siam after Sukhothai. It was founded in 1350 and destroyed by Burmese in the 18th century. It is a UNESCO World Heritage site and while it was once a cosmopolitan center, it is now a set of ruins similar to Angor Wat in Cambodia. Many of the original statues were damaged but some parts remain. Photos below are of Wat Maha That or the Monastery of the Great Relic, built in the 14th century.
Below is Wat Chaiwattharanam, next to the Chao Phraya River. It was built in Khmer style in 1630 by King Prasat Thong and was abandoned after the Burmese attacked the city in 1767. It is not part of the Ayutthaya Historical Park.