The Mường (Vietnamese: Người Mường) is the third largest of Vietnam's 53 minority groups, with an estimated population of 1.3 million (based on the 2009 census and five years of population growth). The Muong people inhabit the mountainous region of northern Vietnam, concentrated in Hòa Bình Province and the mountainous districts of Thanh Hóa Province. They are most closely related to the ethnic Vietnamese. While the Muong are believed to be related to the Vietnamese, some ethnologists theorize the Muong remained in the mountains and developed independently while the Vietnamese moved to the low country and became influenced by Chinese culture resulting from the 111 BC invasion by Chinese Han Emperor Wu Ti. The Muong and the Tai have had a mutual influence on each other's culture, so today the Muong are ethnically and linguistically close to the Vietnamese, but culturally and socially similar to the Tai.