The Tran ruled the Trần dynasty, a golden age in Vietnam, and successfully withheld the Mongol invasions of Vietnam, introducing improvements to Chinese gunpowder. During the Tran dynasty, the arts and sciences flourished, and Chữ Nôm was used for the first time in mainstream poetry. Emperor Trần Nhân Tông was a great reformer of Chu Nom and the first emperor to use Chu Nom in Vietnamese poetry.