Prambanan is the largest Hindu temple of ancient Java, and the construction of this royal temple was probably started by Rakai Pikatan as the Hindu Sanjayas answer to the Buddhist Sailendra’s Borobudur and Sewu temples nearby. The construction of Prambanan probably was meant to marked the return of Sanjaya dynasty to power after almost a century fell under Sailendra domination on Central Java.
A temple was first built at the site around 850 CE by either Rakai Pikatan or Balitung Maha Sambu the Sanjaya king of the Mataram Kingdom. According to Shivagrha inscription that wrote chandrasengkala ”Wwalung gunung sang wiku” (778 Saka/856 M), the temple was built to honor lord Shiva and the original name of the temple is Shiva-grha (the house of Shiva).[2] Indeed, some archaeologists propose that the idol of Shiva in the garbhagriha (central chamber) of the main temple is modelled after King Balitung, serving as a depiction of his deified self after death.[3].
The temple compound was expanded by successive Mataram kings such as Daksa and Tulodong with the addition hundreds of perwara temples around the chief temple. Prambanan served as the royal temple of the Hindu Kingdom of Mataram, with most of the state’s religious ceremonies and sacrifices being conducted there. At the height of the Mataram kingdom, scholars estimate that hundreds of Brahmins with their disciples lived within the outer wall of the temple compound. The urban center and the court of Mataram were located nearby, somewhere in the Prambanan valley.  (Source: http://en.wikipedia.org/wiki/Prambanan) Nov.7, 2009.