1794: Market Square, or the "Diamond," is part of the original plan of lots and streets laid out by George Woods and Thomas Vickroy, surveyors from Philadelphia.
Mid-1790s: The first Allegheny County Courthouse is constructed in Market Square
Mid-1910s: The Diamond Market is constructed, and for the first time, Diamond Street passes through the Square and intersects with Market Street. The Diamond Market occupies all four quadrants and has a roller skating rink on the top floor.
1961: The Diamond Market is demolished.
1972: Market Square is designated by the City as its first historic district.
1984: PPG Place is built. The five smaller buildings surrounding the 40-story structure are scaled back to keep with the Square's historic area.
Source: Pittsburgh History and Landmarks Foundation, www.phlf.org.