Puukohola Heiau National Historic Site
To maintain law and order, a kapu (taboo) system based on religious and practical beliefs was imposed by the sovereign ali'i on all of the population. The kapu system was extremely restrictive and rigid, with severe, penalties for those who broke a kapu. The kapu system was in effect for many centuries before it was officially overthrown in 1819, after the death of Kamehameha.
Within this social and religious structure, the political rise of Kamehameha I and the construction of Pu'ukohola Heiau occurred around 1790. Heiau (temples) took on many forms from simple stone markers such as those used as fishing shrines, to massive stone platforms associated with human sacrificial temples. Large heiau such as Pu'ukohola could only be accessed by the priests and chiefly classes.
Kapoukahi, a powerful kahuna from Kauaii, prophesized that war would end if Kamehameha constructed a heiau dedicated to the war god Ku at Pu'ukohola. In 1791, Keoua, Kamehameha’s cousin, was slain at Pu'ukohola, an event that according to prophesy, led to the conquest and consolidation of the islands under the rule of Kamehameha I.
Learn more here. http://www.nps.gov/puhe/index.htm