Pittsburgh is a city located in the US state of Pennsylvania. Pittsburgh Center is located at the confluence of the Allegheny and Monongahela rivers, which together are the sources of the Ohio River. Thanks to its location, the downtown resembles a triangle. The U.S. Steel Tower, One Mellon Center, PPG Place, Oxford Center and Highmark Place are the highest skyscrapers in Pittsburgh. A lot of emigrants from Poland settled in Pittsburgh in the 19th century – the Polish Hill district with the Polish church are reminders of that time.