Location
Bayon temple is a magnificent stone structure situated at the exact center of Angkor Thom (literally: “Great City”), which signifies the conjunction of heaven and earth. Angkor Thom is Jayavarman VII’s capital and was the last and most enduring capital city of the Khmer empire. It is much larger in size comparing to the world-famous Angkor Wat and comprises not only Bayon, but also some other famous spots such as The Terrace of the Leeper King and Baphuon temple. Bayon temple is 10km from Siem Reap city center and 2km from Angkor Wat. The map below shows the layout of the Angkor Archaeological Park:

Map showing Angkor Thom

 

Religion
Bayon is the only Angkorian state temple dedicated to Mahayana Buddhism. However, after Jayavarman VII’s death, the temple was modified by subsequent Hindu and Theravada Buddhist kings to suit their own religious preferences.

Origin
To understand the importance and origin of the Bayon temples, it is essential to have a grasp of the regime of King Jayavarman VII. It was during the late 12th and early 13th century that the Bayon was built under the rule of King Jayavarman VII, a century after Angkor Wat was built by Suryavarman II. Jayavarman VII was a respected and celebrated king as he led a local army to oust the invaders and to secure the capital of Cambodia. Jayavarman VII was a staunch believer of Mahayana Buddhism and dedicated his reign as king in the service and upliftment of his subjects.
Jayavarman VII was instrumental in creating a grand program of constructing public works and monuments. As part of this program, he first built hospitals, schools, reservoirs, rest houses for pilgrims and other public benefiting works. The second step was to build Ta Prohm temple in honor of his mother and Preah Khan in honor of his father. To mark the completion of the grand construction program, Jayavarman VII built the “Temple – Mountain” at Bayon and developed the city around it.

Characteristics of Bayon
Occupying an area of 9 square kilometer, the Bayon temple’s entrance faces the east.
The temple comprises two galleried enclosures and an upper terrace. The two galleried enclosures bear over 11,000 carved figures depicting legendary and historical events of the Khmer empire. Some of the must-see carvings include:
The All-seeing King – The carvings show a giant fish swallowing an antelope and a prawn hiding among smaller fish, indicating that the king will seek out those in hiding.
A Khmer Circus- This group of panels shows a man holding three dwarfs, a man lying on his back and spinning a wheel with his feet, a group of tightrope walkers and the royal court watching all these from a terrace.
The Chams sack Angkor – This panel on the east wall depicts the war of 1177 in which the Angkor was defeated.

Khmer Circus

 Of course, the Bayon is renowned for is its 216 gigantic faces on the temple’s 54 towers. There are various schools of thoughts regarding whom those faces represent. Some scholars believe that they represent King Jayavarman VII himself while others say they belong to boddhisattva Avalokiteshvara. The curious smiles of these faces have been dubbed as the “Mona Lisa of Southeast Asia.”

In 2010, a team of Cambodian and Japanese archaeologists uncovered an ancient man-made drainage system at the site of the Bayon temple, the first time such a drainage system has been discovered.
 

Conservation and Restoration
The Bayon temple is one of the most endangered monuments among all Angkor monuments. It is also the most technically challenging one to restore.
The first restoration work was led by the École Française d’Extrême Orient in the early 20th century. Since 1995, the Japanese Government team for the Safeguarding of Angkor has been the main conservatory body.

References:
http://en.wikipedia.org/wiki/Bayon
http://www.angkor-jsa.org/main_e.html
http://www.tourismcambodia.com/attractions/angkor/bayon.asp
http://home.planet.nl/~bellaart/html/cambodia/awtsub6.htm
Lonely planet Cambodia – Nicky Ray