Dong Phaya Yen or Dong Phya Yen (, , lit. "jungle of the cold lord") is a mountain range in Phetchabun, Chaiyaphum, Lopburi, Saraburi, and Nakhon Ratchasima Provinces, Thailand. As the Dong Phaya Yen is less compact and lower in height than the mountain ranges to the north and to the south, the first roads and railroads connecting the region of Isan with the capital Bangkok were built across these mountains. Before the construction of the railroad at the beginning of the 20th century, communication between these two parts of Thailand was difficult. The survey for the building of the Northeastern Line of the State Railway of Thailand began in 1887. Geography The Dong Phaya Yen Mountains consist mainly of a range of scattered medium-height hills stretching southwards of the Phetchabun Mountains in an arch until reaching the northern side of the Sankamphaeng Range. The mountain chain has a length of about 170 km and reaches a maximum elevation of 1,167 m at Phu Khing at the northern end. Other peaks are 900 m high Khao Phang Yai, 767 m high Khao Kheuan Lan, 782 m high Khao Cham Dot, 718 m high Khao Chalong Tong, 745 m high Khao Chan Luang, 722 m high Khao Lom, 722 m high Khao Sawong, 721 m high Khao Wong Chan Daeng, 689 m high Khao Phrik, 695 m high Khao Somphot, 657 m high Khao Kradon, 676 m high Khao Inthaya, 683 m high Khao Mot Ngam, 655 m high Khao Plai Khlong Kum, and 575 m high Khao Sadao. The northern limit of the Phetchabun massif is not clearly defined, roughly beginning south of the 16th parallel north where the ranges forming the Phetchabun system become a group of scattered mountains of lesser height, rarely surpassing 800 m, extending southwards. The eastern mountain chain of the Phetchabun Range is mentioned as the "Phang Hoei Range" in some geographical works, a name that encompasses the whole northern section of the Dong Phaya Yen mountain system, for Khao Phang Hoei is a 1,008 m high summit west of Chaiyaphum town, beyond the southern end of the Phetchabun Range proper in the northern half of the Dong Phaya Yen. The Dong Phaya Yen range divides the Chao Phraya river valley of central Thailand and the Khorat Plateau of the northeast. The mountains are drained to the east by several tributaries to the Chi and