dating from early 13th century AD. The inscription was carved on a stone stele, in combined Chữ Hán and archaic form of the Chữ Nôm. In the distant past, Vietnamese shared more characteristics common to other languages in South East Asia and with the Austroasiatic family, such as an inflectional morphology and a richer set of consonant clusters, which have subsequently disappeared from the language under Chinese influence. Vietnamese is heavily influenced by its location in the Mainland Southeast Asia linguistic area, with the result that it has acquired or converged toward characteristics such as isolating morphology and phonemically distinctive tones, through processes of tonogenesis. These characteristics have become part of many of the genetically unrelated languages of Southeast Asia; for example, Tsat (a member of the Malayo-Polynesian group within Austronesian), and Vietnamese each developed tones as a phonemic feature. The ancestor of the Vietnamese language is usually believed to have been originally based in the area of the Red River Delta in what is now northern Vietnam. Distinctive tonal variations emerged during the subsequent expansion of the Vietnamese language and people from the Red River Plain into what is now central and southern Vietnam through conquest of the ancient nation of Champa and the Khmer people of the Mekong Delta in the vicinity of present-day Ho Chi Minh City, also known as Saigon. Northern Vietnam was primarily influenced by Chinese, which came to predominate politically in the 2nd century BC. After the emergence of the Ngô dynasty at the beginning of the 10th century, the ruling class adopted Classical Chinese as the formal medium of government, scholarship and literature. With the dominance of Chinese came radical importation of Chinese vocabulary and grammatical influence. The resulting Sino-Vietnamese vocabulary makes up about a third of the Vietnamese lexicon in all realms, and may account for as much as 60% of the vocabulary used in formal texts. After France invaded Vietnam in the late 19th century, French gradually replaced Chinese as the official language in education and government. Vietnamese adopted many French terms, such as ('dame', from ), ('train station', from ), ('shirt', from ), and ('doll', from ). Henri Maspero described six periods of the Vietnamese language: Proto-Viet–Muong, also known as Pre-Vietnamese, the ancestor of Vietnamese and the related Mường language (before 7th century AD). Proto-Vietnamese, the oldest reconstructable version of Vietnamese, dated to just before the entry of massive amounts