After the unification of the peninsula up to Taedong River in 668 AD, Gyeongju became the center of Korean political and cultural life. The city was home to the Silla court, and the great majority of the kingdom's elite. Its prosperity became legendary, and was reported as far away as Persia according to the 9th century book, "The Book of Roads and Kingdoms". Records of "Samguk Yusa" give the city's population in its peak period as 178,936 households, suggesting that the total population was almost one million. Many of Gyeongju's most famous sites date from this period, known as Unified Silla.