Located at the foot of Nangsan Mountain in Gyeongju, this temple site stands directly opposite Sacheonwangsa Temple. It is not known exactly when the temple was built, although some historians insist that it was built during the reign of King Sinmun (r. 681-692) or King Munmu (r. 661-681) of Silla. According to Samguk yusa (Memorabilia of the Three Kingdoms), Sacheonwangsa Temple was built in 679 to supplicate Buddha's aid for the protection of Silla against the mighty Tang armies of China that were poised to invade the kingdom. Upon hearing about the new temple, Tang sent an envoy to ascertain the veracity of the news. Silla, then, hurriedly built this temple opposite the site of Sacheonwangsa Temple and named it Mangdeoksa Temple, meaning that the temple was made to thank the Tang Dynasty for its virtue.
There were other fantastic stories about the temple, one of which asserts that in 755 the pagoda of the temple swayed heavily to warn Silla of the An Shi Rebellion (755-763) which would shake Tang society to the core. According to the stories in Samguk yusa, King Hyoso (r. 692-702) was derided at a banquet held to celebrate the opening of the temple because he failed to see the Shakyamuni’s “true dharma body” which revealed itself during the banquet. In another story, a monk named Seonyul died of hard work in the middle of copying the Heart Sutra, but was sent back to Earth from the underworld so that he could complete the work.
The site shows that the temple had two wooden pagodas to the east and west of the courtyard, which was enclosed by galleries, a main prayer hall, a lecture hall, and a middle gate, displaying the typical twin-pagoda layout prevalent during the Unified Silla Era. The site also contains a pair of flagpole supports (Treasure) and the vestiges of a stairway to the south of the middle gate. Historians consider the temple one of the three most important temples in Gyeongju along with Hwangnyongsa and Sacheonwangsa Temples.