Gyeongju was the capital of the ancient kingdom of Silla (57 BC – 935 AD) which ruled about two-thirds of the Korean Peninsula between the 7th and 9th centuries. Later Silla was a prosperous and wealthy country, and its metropolitan capital of Gyeongju was the fourth largest city in the world.[10][11][12][13] A vast number of archaeological sites and cultural properties from this period remain in the city. Gyeongju is often referred to as "the museum without walls".[14][15] Among such historical treasures, Seokguram grotto, Bulguksa temple, Gyeongju Historic Areas and Yangdong Folk Village are designated as World Heritage Sites by UNESCO.[16][17] The many major historical sites have helped Gyeongju become one of the most popular tourist destinations in South Korea.[18]