Towards the middle 15th century, the city state of Ayudhaya acceded power from Sukhothai and became the new seat of government for the Thai people for a total of 417 years. The city had been founded on an island at the junction of three rivers. The lowlands surrounding the city flooded annually and was rich in alluvial soil. These natural conditions made Ayudhaya strategically easy to defend. Moreover, being near the Chao Phraya estuary made it accessible by seafaring trading vessels. Thus Ayudhaya became an important trading centre controlling foreign trade with all points northward. It quickly achieved a remarkable state of prosperity. Availability of foreign technology and weaponry also made it immensely powerful among its neighbours.
Ayudhaya rule was based on a concept of kingship different to that of Sukhothai. The king was the incarnation of a deity as derived from the Khmer concept. The patriarchal system became a feudal community centre in which all cultural activities and services took place. The king became the royal patron of the Buddhist faith, as well as of all the arts.
Ayudhaya's income were from its beutiful agricultural products, and from duties levied against foreign trade. Merchants came from China, Java, Malaya, India, Sri Lanka, Persia, Japan, Portugal, France, Holland and England. At its height, Ayudhaya became one of the most important trading centres in the area. Its prosperity may be witnessed from its arts, many aspects of which reached perfection unmatched in Thai history Sukhothai culture. Finally, during the mid 17th century, a new `chedi' form appeared which was square in plan with multiple redented corners. This Thai development of an ancient architectural form continued to be built throughout the rest of the Ayudhaya period and into the Bangkok period.
Likewise, Ayudhaya painting developed in three distinct phases. During the early period, the paintings displayed strong Khmer origins. Only three colours were known and used : red, black and white. Remnants of paintings of this early period show juxtaposed rows of Buddha figures, and ornamental frames presumably backdrops for Buddha statues. The middle period of Ayudhaya painting exhibits Sukhothai influence, as may be seen in surviving illustrated manuscripts `lai rod nam'. This made possible the application of extremely thin leaves of gold on a lacquer background in free-form designs. It was used to decorate all things considered valuable from book binders to whole buildings.
Ayudhaya fell to an invading Burmese army in 1767. This was the culmination of decades of armed conflict between the two countries. The once glorious city was left devastated and without leadership. It was abandoned and quickly went into ruin. The fall of Ayudhaya was so catastrophic that decades after the event, Thais reminisced about "the glorious old city.