The Royal Pantheon, called Prasat Phra Thep Bidorn in Thai, is the largest building on the upper platform. It was built on the east end of the platform, next to the Phra Mondop, by King Rama IV. It was originally intended to house the Emerald Buddha. King Rama IV observed that the Phra Mondop on its elevated platform occupied a higher position that the Emerald Buddha. He ordered the new building constructed on the platform, which was extended to accommodate it. Unfortunately, the building proved too small and the plan to have it house the Emerald Buddha was abandoned.