The Inca society was the society of the Inca civilization in Peru. The Inca Empire, which lasted from 1438 to 1533 A.D., represented the height of this civilization. The Inca state was known as the Kingdom of Cusco before 1438. Over the course of the empire, the rulers used conquest and peaceful assimilation to incorporate a large portion of western South America, centered on the Andes mountain ranges. The empire proved relatively short-lived however: by 1533, Atahualpa, the last Sapa Inca (emperor) of the Inca Empire, was killed on the orders of the conquistador Francisco Pizarro, marking the beginning of Spanish rule. The last Inca stronghold, the Neo-Inca State in Vilcabamba, was conquered by the Spanish in 1572. Population Population estimates for the Tawantinsuyu society range from as few as 4.1 million people to more than 36 million. Most estimates are between 6 and 14 million people. The reason for these various estimates is that, while the Inca kept excellent census records using their quipus, knowledge of how to read them has been lost. Almost all of them were destroyed by the Spanish in the course of their conquest and rule. Marriage Women and men had parallel roles, but were separate in Inca society. They were equally valued for the part they played in their society despite their differing roles. Marriage was no different. Inca women were typically married at the age of sixteen, while men married at the age of twenty. Age, however, was not as important as keeping track of the stage of life that a person was at, such as whether or not they were able to work or be married. Ranks played a role in a person's marriage status as well. Men of lower rank could only have one wife; people of higher ranks than the kuraka were allowed more. If a man had more than one wife, one served as the principal wife while the others were considered secondary. Having more wives showed that the man had more labor showing that the household was wealthy. The death of the principal wife was sometimes met with the suspicion that the husband played a role in her death. The man had to find a new principal wife before he was able to recover from the previous wife's death. To prevent such suspicion and to increase the likelihood of a successful marriage, there were situations in which the