sentences:  At the start of the 20th century, City of Pittsburgh and Allegheny County officials began to realize that the current structure which housed the city and county government offices was insufficient for the city's rapid growth.The offices at that time were located in the Smithfield Street City Hall building, which was built in 1868-1872.The demand for new offices grew exponentially with the incorporation of Allegheny City into the City of Pittsburgh in 1907, which added 130,000 new residents to the city.