The Bayon's most distinctive feature is the multitude of serene and massive stone faces on the many towers which jut out from the upper terrace and cluster around its central peak. Khmer Smile refers to this mystic grin of King Jayavarman VII who ruled Cambodia in the 12th Century. During his reign, the Khmers built the famous Bayon Temple in Angkor Thom. It is generally believed this portrait is a combinatiion of Boddhisattva Avalokitesvara and King Jayavarman VII himself. To show his omnipresence and omnipotence, his face was carved in facets of all the towers in the Bayon Temple such that his subjects can see his compassionate look and enlightened smile. 

巴戎廟位於吳哥城中央，為當時之國廟，建於800年前，以中小型石塊堆疊成49座高塔，每座塔都雕有四面佛，像徵眼觀四面，耳聽八方。中心塔群象徵宇宙中心的須彌山，身處其中，視線離不開佛像，佛像據說是興建此廟的國王與菩薩的合體，慈祥閉目，咀角含笑，這個地方就被稱為「高棉徵笑」。

http://en.wikipedia.org/wiki/Bayon