I) Prehistoric epoch (early first millennium BCE to seventh century CE)
The first phase of the prehistoric epoch includes those sites that were founded in the early Iron Age (first half of first millennium BCE), and the developed Iron Age (middle and late first millennium BCE) of Inner Asia. Possibly, late Bronze Age (circa 1200 to 800 BCE) affiliations are also indicated in the first phase of prehistoric Tibetan civilization, but this remains difficult to corroborate.1 A treatment of more remote prehistoric epochs (Paleolithic, Mesolithic, Neolithic) falls outside the purview of the current study.2 The second or later phase of the prehistoric epoch corresponds to an anachronistic extension of the Iron Age, marked by the Central Tibetan line of kings (late first millennium BCE to the seventh century CE). This second phase of the prehistoric epoch can be termed the protohistoric or legendary monarchal period, due to the many Tibetan literary records that refer to the Central Tibetan kings of that time. There are also Bön texts purported to have been written in this time frame, though solid evidence for this allegation is lacking. These literary records include some assumed to have been first written in the Zhangzhung and Sumpa languages, which came to be translated into Tibetan during the imperial period. According to the Tibetan historical tradition, the plateau of the Iron Age was divided into a number of petty states and governed by a succession of demigod chieftains. The protohistoric period in turn, is marked by the rise of the yar lung or Pugyel dynasty beginning with King Nyatri Tsenpo (traditional chronologies place him in the circa 200 BCE period).