Over the past 3,000 years, the city of Beijing has had numerous other names. The name ''Beijing'', which means "Northern Capital" (from the Chinese characters  for ''north'' and  for ''capital''), was applied to the city in 1403 during the Ming dynasty to distinguish the city from Nanjing (the "Southern Capital"). The English spelling ''Beijing'' is based on the government's official romanization (adopted in the 1980s) of the two characters as they are pronounced in Standard Mandarin. An older English spelling, ''Peking'', is the postal romanization of the same two characters as they are pronounced in Chinese dialects spoken in the southern port towns first visited by European traders and missionaries. Those dialects preserve the Middle Chinese pronunciation of  as ''kjaeng'', prior to a phonetic shift in the northern dialects to the modern pronunciation. Although Peking is no longer the common name for the city, some of the city's older locations and facilities, such as Beijing Capital International Airport, with the IATA Code PEK, and Peking University, still retain the former romanization.