The population of Amman reached 4,007,526 in 2015; the city contains about 42% of Jordan's entire population. It has a land area of  which yields a population density of about . The population of Amman has risen exponentially with the successive waves of immigrants and refugees arriving throughout the 20th century. From a population of roughly 1,000 in 1890, Amman grew to around 1,000,000 inhabitants in 1990, primarily as a result of immigration, but also due to the high birthrate in the city. Amman had been abandoned for centuries until hundreds of Circassians settled it in the 19th century. Today, about 40,000 Circassians live in Amman and its vicinity. After Amman became a major hub along the Hejaz Railway in 1914, many Muslim and Christian merchant families from al-Salt immigrated to the city. A large proportion of Amman's inhabitants have Palestinian roots (urban or rural origin), and the two main demographic groups in the city today are Arabs of Palestinian or Jordanian descent. Other ethnic groups comprise about 2% of the population. There are no official statistics about the proportion of people of Palestinian or Jordanian descent.