text: Ruins built in this empire's first capital are called the Roluos Group.
full_question: Ruins built in this empire's first capital are called the Roluos Group. An expedition by Henri Mouhot spurred Western interest in this empire, which one man ascended to rule by jumping on the head of a rival's war elephant and killing him. Legendarily, this empire's founder declared independence from Sailendra before he absorbed the pre-existing Chenla people. Leaders called chakravartin led this empire, which built massive water reservoirs called baray. Many complexes built by this empire, such as Bayon, represented the mythical Mount Meru. This empire, whose boats fought against Champa on the Tonle Sap, was founded by Jayavarman II. For 10 points, name this Hindu-turned-Buddhist medieval empire which built Angkor in what's now Cambodia.
first_sentence: Ruins built in this empire's first capital are called the Roluos Group.
raw_answer: Khmer Empire [do not accept "Khmer Rouge"]