The Boston Public Library's posted this ad for the Providence and Boston train station that once sat where Columbus Avenue today enters Park Square - and which replaced an even older station. Note on this map that its tracks crossed the line of the Boston and Albany just before the station.
Here's a photo from sometime after its construction in 1872 - note the Lincoln statue, which remains in the square, although not in the same prominent location:
Back then, of course, trolley lines ran through the square.
The station didn't last that long - here's a photo of Park Square in 1905, as the future home of Paine Furniture (note Trinity and Old South churches in the upper left; also see the square in 1900):
Park Square eventually became dominated by cars, as shown in these Leslie Jones photos from sometime before the construction of the Motor Mart building (note the Lincoln statue's prominent location in the square and that the second photo shows the Hotel Statler, later renamed the Park Plaza):
Also see: Lightning striking near the hotel in 1930.
Eventually, the parking lot (Another view) was replaced by the Motor Mart, which was the largest parking garage in the world when built in 1927. Here's a Jones photo from 1932 (here's an aerial shot from 1928):
The roof of the Motor Mart briefly doubled as a helicopter terminal.
Park Square once had a Trailways bus depot.
More Park Square photos from the BPL.
BPL photos posted under this Creative Commons license.