This week, the Royal Ballet of Cambodia comes to the Brooklyn Academy of Music, where the company will perform the The Legend of Apsara Mera. This dance epic is made up of two stories, both of them deeply embedded in the Cambodian cultural identity, the Churning of the Sea of Milk, and the Legend of Kambu and Mera. Both are foundation myths: one about the creation of the universe, the other about the birth of the Khmer. They will be interpreted in the highly codified, graceful language of Cambodian classical dance, an art form which almost disappeared during the period of the Khmer Rouge (1975-1979). Now, after years of painstaking reconstruction, the nation’s dance culture has been restored. It faces what is perhaps a more insidious threat: modern life.