Short answers, pulled from the story.
Angkor Thom was established in the late twelfth century by King Jayavarman VII as the capital of the Khmer Empire. It was his most ambitious building project, and an inscription found in the city described Jayavarman as the groom and the city as his bride.
Angkor Thom means "Great City." The name derives from the Khmer word Thom, meaning big or great, combined with a form of the Sanskrit word Nagara, meaning city. The name Angkor Thom came into documented use from the 16th century, though the site had earlier been known as Yasodharapura.
Angkor Thom enclosed an area of 9 square kilometers, with laterite walls 8 meters high and 3 kilometers long on each side, flanked by a moat. The city is believed to have sustained a population of 80,000-150,000 people.
The Ayutthaya Kingdom, led by King Borommarachathirat II, sacked Angkor Thom and forced the Khmer king Ponhea Yat to relocate the capital to Phnom Penh. The city was abandoned sometime before 1609, when a western visitor described it as uninhabited.
The Bayon is the state temple of King Jayavarman VII, located at the geometric center of Angkor Thom. Roads from each of the city's cardinal gates lead directly to it. Archaeologists interpret the city's walls and moat as representing the cosmic ocean and mountains surrounding the Bayon's sacred Mount Meru.
The last temple known to have been constructed in Angkor Thom was Mangalartha, dedicated in 1295. After that date, new structures were built only in perishable materials and none have survived.