Population
There is some debate about the number of people inhabiting Tawantinsuyu at its peak, with estimates ranging from as few as 4 million people, to more than 37 million. The reason for these various estimates is that in spite of the fact that the Inca kept excellent census records using their quipu, knowledge of how to read them has been lost, and almost all of them had been destroyed by the Spaniards in the course of their conquest.
Language
Since the Inca Empire lacked a written language like English, the empire's main form of communication and recording came from quipus, ceramics and spoken Quechua, the language the Incas imposed upon the peoples within the empire. The plethora of civilizations in the Andean region provided for a general disunity that the Incas needed to subdue in order to maintain control of the empire. While Quechua had been spoken in the Andean region, like central Peru, for several years prior to the expansion of the Inca civilization, the type of Quechua the Incas imposed was an adaptation from the Kingdom of Cusco (an early form of "Southern Quechua" originally named Qhapaq Runasimi = The great language of the people) of what some historians define as "Proto-Quechua" or Cusco dialect (the original Quechua dialect).
