Rawalpindi is the third-largest city in the Pakistani province of Punjab. It is a commercial and metropolitan city, being the fourth most populous in Pakistan. It is located near the Soan River in north-western Punjab, and is the third-largest Punjabi-speaking city in the world. Rawalpindi is situated adjacent to Pakistan's capital Islamabad, and the two are jointly known as "twin cities" because of the social and economic links between them. Prior to Islamabad's establishment, Rawalpindi served as the country's capital from 1959 to 1967.