chinese characters were introduced to vietnam after the han empire conquered the country in 111 bc. independence was achieved in 939, but the chinese writing system was adopted for official purposes in 1010. soon after the country achieved independence, vietnamese began to use chinese characters to write their own language. the van ban bell, engraved in 1076, is the earliest known example of a nôm inscription. nguyen thuyen composed nôm poetry in the 13th century. however, none of his work has survived. the oldest surviving nôm text is the collected poetry of king tran nhan tong, written in the 13th century.