Wat Thammikarat temple ruins. The dilapidated remains of a large, early Ayutthayan, octagonal chedi surrounded by stucco and brick lions, or singhas. Ayutthaya was the most powerful kingdom in Siam in the mid-14th century. Its end came after years of conflict, when the capital was sacked by the Burmese in 1767. Today, Ayutthaya Historical Park is a UNESCO World Heritage Site.