Angkor Thom is another site not to miss on your visit to Siem Reap. It is not as well known as Angkor Wat but is just as amazing. Angkor Thom was established in the late 12th century by king Jayavarman VII. It covers an area of 9 km², including several monuments from earlier eras as well as those established by Jayavarman and his successors. At the centre of the city is Jayavarman's state temple, the Bayon, with the other major sites clustered around the Victory Square immediately to the north.

The last temple known to have been constructed in Angkor Thom was Mangalartha, which was dedicated in 1295. Thereafter the existing structures continued to be modified from time to time, but any new creations were in perishable materials and have not survived. In the following centuries Angkor Thom remained the capital of a kingdom in decline until it was abandoned some time prior to 1609, when an early western visitor wrote of an uninhabited city, "as fantastic as the Atlantis of Plato" which some thought to have been built by the Roman emperor Trajan. (Higham 140) It is believed to have sustained a population of 80,000-150,000 people.

The city lies on the right bank of the Siem Reap River, a tributary of Tonle Sap, about a quarter of a mile from the river. The south gate of Angkor Thom is 7 km north of Siem Reap, and 1.7 km north of the entrance to Angkor Wat. The walls, 8 m high and flanked by a moat, are each 3 km long. The walls are of laterite buttressed by earth, with a parapet on the top.

The movie, Lara Croft: Tomb Raider, features several characters visiting Angkor Thom during their trip to Cambodia to recover the first piece of the Triangle of Light.