Movable type never replaced woodblock printing in Korea. Indeed, even the promulgation of Hangeul was done through woodblock prints. The general assumption is that movable type did not replace block printing in places that used Chinese characters due to the expense of producing more than 200,000 individual pieces of type. Even woodblock printing was not as cost productive as simply paying a copyist to write out a book by hand if there was no intention of producing more than a few copies. Although Sejong the Great introduced Hangeul, an alphabetic system, in the 15th century, Hangeul only replaced Hanja in the 20th century. And unlike China, the movable type system was kept mainly within the confines of a highly stratified elite Korean society: